feed's  Series  of  Pocket 


01  i 


v/ 

PHYSIOLOGY; 


A  MANUAL  FOR  STUDENTS  AND  PRACTITIONERS, 


BY 


HOWARD   D.  COLLINS,  M.D., 

Assistant  to  the  Attending  Surgeon  of  the  Roosevelt  Hospital ;  Assistant  Demonstrator  of 
Anatomy,  College  of  Physicians  and  Surgeons  (Columbia  University),  New  York. 


WM.  H.  ROCKWELL,  JR.,  M.  D., 

Assistant  Demonstrator  of  Anatomy,  College  of  Physicians  and  Surgeons  (Columbia 
University),  New  York;  Member  of  Association  of  American  Anatomists. 


SERIES   EDITED  BY 

BERN    B.   GALLAUDET,   M.D., 

Demonstrator  of  Anatomy  and  Instructor  in  Surgery,  College  of  Physicians  and  Surgeons, 
Columbia  University,  New  York;  Visiting  Surgeon,  Bellevue  Hospital,  New  York. 

ILLUSTRATED  WITH  ONE  HUNDRED  AND  FIFTY-THREE  ENGRAVINGS. 


LEA   BROTHERS  &  CO., 
PHILADELPHIA    AND    NEW    YORK. 


Entered  according  to  Act  of  Congress,  in  the  year  1899,  by 

LEA  BROTHERS  &  CO., 
In  the  Office  of  the  Librarian  of  Congress,  at  Washington.    All  rights  reserved. 


WESTCOTT    4    THOMSON, 
ELECTROTYPFRS.   PHILADA. 


PREFACE. 


IN  preparing  the  present  volume  the  authors  make  no  claim 
to  original  research.  Their  purpose  is,  frankly,  not  only  to 
help  the  student  acquire  a  knowledge  of  physiology  such  as 
will  enable  him  to  read  with  better  understanding  the  larger 
works  on  the  subject ;  but  also  to  give  him  actually  fuller  and 
more  accurate  information  than  can  be  obtained  from  the 
various  and  popular  quiz-compends. 

Thus,  in  each  section,  in  addition  to  the  purely  physiologi- 
cal aspects,  histological  considerations  are  discussed,  such  as 
those  of  the  cell  in  general  and  of  the  neuron  in  the  nervous 
system  ;  and,  wherever  practicable,  the  application  of  physio- 
logical principles  to  pathological  conditions  is  also  dealt  with. 

Acknowledgment  as  to  source  of  material  is  made  to  the 
larger  works  of  Chapman,  Kirke,  and  Foster,  to  the  manual 
by  Dr.  F.  A.  Manning,  and  to  the  lectures  delivered  at  the 
College  of  Physicians  and  Surgeons  of  New  York. 

HOWARD  D.  COLLINS, 
WM.  H.  KOCKWELL,  JR. 


• 


CONTENTS. 


PAGE 

GENERAL  CONSIDERATIONS:  Physiology;  life;  living  body  com- 
pared to  a  machine ;  metabolism 17,18 

CELLS  :      Structure  ;     gemmation  ;     karyokinesis  ;     development ; 

amoeba ;   classification  of  tissues 18-24 

CHEMISTRY   OF  THE   BODY  :    Proximate  principles ;    inorganic ; 

organic 24-30 

THE  BLOOD:  Gross  appearance ;  quantity;  red  corpuscles  ;  func- 
tion; globulin;  hsematin ;  leukocytes;  lymphocytes;  func- 
tion ;  blood-plates  ;  plasma  ;  serum  ;  gases  ;  coagulation  .  .  .  30-46 

THE  LYMPH:  Composition;  sources;  uses 46-48 

CIRCULATION  OF  THE  BLOOD:  Apparatus;  course;  heart;  action 
of  auricles  and  ventricles  ;  capillaries  ;  veins  ;  arteries ;  speed  ; 
blood-pressure;  arterial  tension;  the  blood  in  circulation; 
action  of  heart ;  systole ;  diastole ;  arterial  tension  ;  heart- 
sounds  ;  heart-innervation  ;  vaso-motor  nerves ;  pulse ;  sphyg- 
mograph 48-70 

"CIRCULATION"  OF  THE  LYMPH:  Lymphatics;  stomata  and 
pseudostomata ;  flow  of  lymph ;  sources ;  pressure ;  lymph- 
ganglia  70-75 

RESPIRATION  :  Respiratory  act ;  movements  ;  tract ;  larynx  ; 
trachea  ;  bronchi ;  lungs ;  muscles  :  of  inspiration  ;  of  expira- 
tion ;  forced  inspiration;  forced  expiration  ;  sounds;  tidal  air; 
reserve  air  ;  residual  air ;  complementary  air ;  expired  air ; 
external  respiration ;  internal  respiration  ;  nervous  mechan- 
ism ;  centres ;  section  of  vagi  ;  vitiated  atmosphere ;  effect  of 

respiration  on  circulation  ;    special  respiratory  acts 75-90 

5 


6  CONTENTS. 

PAGE 

DIGESTION:  Mouth;  mastication;  teeth;  saliva;  ptyalin;  deglu- 
tition; stomach;  gastric  juice  ;  peptones;  gastric  digestion  ; 
vomiting;  small  intestine;  intestinal  digestion;  intestinal 
juice;  the  pancreas  ;  pancreatic  juice  ;  trypsin  ;  amylopein; 
steapsin  ;  the  liver;  secretion  of  the  liver;  bile;  bile-salts; 
bile-pigments  ;  cholesterin  ;  excretion  of  the  liver ;  glycogenic 
function  ;  large  intestine  ;  defecation  .  90-108 

ABSORPTION:  Dialysis;  sites  of  absorption;  villi  of  intestine; 
changes  in  the  products  of  digestion  on  being  absorbed ;  des- 
tination of  absorbed  food 109-112 

SECRETION  :  Secretions  ;  excretions  ;  apparatus  ;  glands  ;  dis- 
charge ;  correlation  of  secretions  ;  serous;  mucous;  mammary 
glands  ;  milk  ;  secretions  of  skin  ;  structure  of  skin  ;  seba- 
ceous glands  ;  sweat-glands;  hair;  nails;  sweat;  perspiration; 
absorption  by  skin;  kidneys;  structure  of  kidneys;  blood- 
supply;  ureters;  bladder;  urine;  secretion  of  urine ;  compo- 
sition ;  acidity  of  urine  ;  course  of  urine  ;  amount ;  micturi- 
tion ;  urea;  uric  acid  ;  vascular  glands ;  table  of  secretions  .  .  113-134 

NUTRITION  :  Sources  of  income  to  the  body  ;  expenditures  of  the 
body;  energy  of  the  body:  starvation;  diet;  overfeeding; 
nitrogenous  equilibrium  ;  assimilation 134-138 

ANIMAL  HEAT:  Normal  temperature;  sources  of  heat;  loss  of 
heat ;  regulation  of  heat ;  centres  for  heat-regulation  ;  limits 
of  body-temperature  .  138-140 

MUSCLE  :  Varieties  ;  microscopic  appearances ;  general  properties  ; 
chemistry;  physiology;  muscles  as  levers;  oxygen-supply; 
fatigue  ;  latent  period  ;  contractility  ;  stimuli ;  electrical  cur- 
rents ;  effect  of  galvanic  shock ;  electrical  state ;  excitability 
and  conductivity  ;  Pfliiger's  law  of  contraction  ;  ascending  and 
descending  currents  ;  nerve-muscle  preparation  ;  rigor  mortis  .  140-159 

NERVOUS  SYSTEM:  Fibres  and  cells;  varieties  of  fibres;  nerve- 
trnnks  ;  function  of  fibres  ;  nerve-cells  ;  varieties  ;  nerve-end- 
ing :  nerve-impulse ;  neuron;  speed  of  nerve-impulses; 
degeneration  ;  regeneration 159-169 

Sympathetic  System :  Fibres;  communication  with  cerebro-spinal 
>y-trin  ;  iranylia  ;  pelvic  plexuses ;  function;  vaso-motor  fibres ; 
relation  to  secreting  glands 169-173 


CONTENTS.  7 

PAGE 

Spinal  Cord:  Gross  anatomy;  nerves;  white  substance;  gray 
matter  ;  nerve-roots  ;  trophic  centres ;  functions ;  conduction  ; 
motor  fibres ;  sensory  fibres  ;  transference  ;  reflex  action  ; 
augmentation;  automatic  acts;  coordination;  inhibition.  .  .  174-185 

Medulla  Oblongata:  Anatomy;  columns;  gray  matter  ;  function; 

special  centres 185-191 

Pons,  Crura  Cerebri,  Corpora  Quadrigemina:   Paralysis  following 

lesions;  functions 191,192 

Cerebrum :  Hemispheres ;  fissures;  convolutions;  regions;  lobes; 
gray  matter ;  chemistry  of  brain-tissue  ;  weight  of  brain ; 
course  of  fibres  ;  corpora  striata ;  optic  thalami  ;  functions  of 
cerebrum  ;  localization  of  brain -function  ;  motor  areas  ;  sen- 
sory areas:  paralysis 192-201 

Cerebellum:  Gray  matter  ;  function 201-203 

Tracts  in  Brain  and  Cord :   Motor  tract ;   sensory  tract ;  lesions  .  203,  204 
Mutilations:  Brain;  cord;  cerebellum;  hemispheres 204-206 

Cranial  Nerves:  III  nerve;  IV  nerve;  V  nerve;  VI  nerve; 
VII  nerve;  IX  nerve;  X  nerve;  XI  nerve  ;  XII  nerve  .  .  .  206-220 

THE   SEXSES  :    Sensations  ;    special  ;    common  ;    pain  ;   hallucina- 
tions ;  perceptions;  judgments 220-222 

Touch :  Organ  ;  varieties  ;  acuteness ;  measure  of ;  pressure-sen- 
sation ;  muscular  sense  ;  temperature-sense 222-225 

Taste  :  Tongue ;  papillae ;  taste-globlets ;  association  of  smell ; 
after-taste  .  .  .  225-229 


Smell:  Odors;  olfactory  nerves ;  acuteness  of;  sneezing    ....  229-232 

Hearing :  Auditory  apparatus ;  external  ear ;  middle  ear ;  inter- 
nal ear;  membrana  tympani ;  ossicles;  Eustachian  tube; 
semicircular  canals  ;  sense  of  equilibrium  ;  cochlea  ;  canalis 
cochlearis  ;  sacculi ;  utricle  ;  organ  of  Corti ;  auditory  nerve  ; 
course  of  sound-waves;  localization  of  hearing;  distance; 
subjective  hearing ;  musical  range 232-241 

Voice  or  Speech :  Larynx  ;  production  of  voice ;  articulate 
speech ;  musical  range  of  the  voice  . 241-243 


8  CONTENTS. 

PAGE 

Sight:  Visual  apparatus;  accessory  organs  of  eye;  eyelids; 
lachrymal  gland;  Meibomian  glands;  extrinsic  muscles  of  the 
eye;  eyeball;  cornea;  sclera;  aqueous  humor;  crystalline 
lens;  ciliary  muscle;  iris;  vitreous  humor;  refraction; 
accommodation ;  retina ;  rods  and  cones ;  area  of  most  acute 
vision  ;  blind  spot ;  optic  nerve  ;  optic  tracts ;  nervous  mechan- 
ism of  vision ;  binocular  vision  ;  stereoscope ;  inversion  of 
the  image ;  visual  sensations  and  perceptions ;  retinal  red ; 
optograms ;  achromatism  ;  after-images ;  near-point ;  emme- 
tropic  eye;  myopia;  hypermetropia;  presbyopia;  astig- 
matism; diplopia;  color-blindness;  theories  of  normal  color- 
perception  ;  causes  of  color-blindness  ;  in  sexes ;  test  for  color- 
blindness    243-265 

EMBRYOLOGY:  Reproduction;  Species;  heredity;  methods  of 
reproduction  ;  asexual ;  sexual ;  theory ;  fecundation  ;  copula- 
tion ;  female  organs  of  generation  ;  ovaries ;  Fallopian  tubes  ; 
uterus ;  vagina ;  ovulatiou  ;  menstruation ;  puberty  ;  meno- 
pause; corpus  luteum;  male  generative  organs;  testicles; 
spermatozoa  ;  seminal  vesicles ;  prostate  gland  ;  penis  ;  urethra ; 
impregnation ;  coitus ;  details  of  impregnation 267-283 

Development:  Segmentation;  germinal  membrane;  changes  in 
uterine  lining;  blastoderm;  medullary  groove;  changes  in 
the  mesoblast ;  structures  derived  from :  the  epiblast,  the 
mesoblast,  the  hypoblast  ;sp  lanchnopleure  ;  umbilical  vesicle  ; 
vitelline  duct;  amnion ;  allantois  ;  chorion ;  placenta;  foetal 
and  maternal  blood ;  umbilical  cord ;  foetal  circulation  ;  vitel- 
line circulation;  placental  circulation  ;  area  vasculosa  ;  forma- 
tion of  heart ;  change  from  foetal  to  adult  circulation  ;  vertebral 
column  ;  cranium  ;  face ;  extremities  ;  spinal  cord  ;  nerves  ; 
brain;  vesicles;  folding  of  brain  axis ;  eye;  auditory  appa- 
ratus ;  olfactory  apparatus ;  alimentary  canal ;  salivary  glands ; 
pancreas;  liver;  lungs;  Wolffian  duct;  Miiller's  duct ;  testicle; 
ovary;  Gartner's  duct ;  external  genitals 283-306 

Parturition:  Expulsion  of  the  foetus ;  uterine  contractions ;  char- 
acter of  uterine  contractions 306,  307 

APPENDIX  :   Table  of  development  of  an  embryo ;   chemical  tests 

used  commonly  in  physiological  analysis;  metric  system  .    .    .  309-311 


PHYSIOLOGY. 


GENERAL  CONSIDERATIONS. 

Physiology,  from  the  Greek  yuaiz,  and  /oyo^,  literally  means 
a  discourse  on  nature.  At  present,  however,  the  word  has  a 
more  limited  significance,  meaning  that  branch  of  science 
which  treats  of  the  workings  of  the  healthy  living  body. 

That  portion  of  physiology  discussed  in  the  following 
pages  is  the  physiology  of  the  healthy  living  human  being. 
From  the  very  nature  of  things  it  is  evident  that  every  detail 
of  physiology  cannot  be  studied  on  the  human  subject,  and 
the  deficiency  has  been  supplied  by  analogous  study  on  the 
lower  animals.  In  order  properly  to  understand  physiology, 
it  is  essential  that  the  student  be  somewhat  familiar  with 
anatomy,  or  that  branch  of  science  which  teaches  the  gross 
structure  of  the  body.  To  appreciate  the  workings  of  a 
machine,  at  least  a  superficial  knowledge  of  its  component 
parts  is  necessary. 

Life :  Our  definition  of  physiology  assumes  the  body  to  be 
alive  ;  but  what  life  is,  is  a  very  difficult  subject  to  explain. 
It  may  be  described  as  the  stimulus  which  keeps  active  the 
functions  of  the  body,  the  characteristic  phenomena  exhibited 
by  living  beings.  It  is  really  indefinable ;  for  while  it  is 
readily  possible  to  state  the  differences  between  living  and 
dead  things,  it  is  impossible  to  define  these  differences. 

Living  body  compared  to  a  machine :  The  living  body 
may  be  compared  to  any  piece  of  complex  machinery,  the 
parts  being  carefully  adjusted  to  one  another  and  performing 
their  work  as  long  as  the  proper  stimulus  is  applied.  When 
the  stimulus  fails — and  in  the  case  of  animals  and  plants  the 
stimulus  is  called  life — the  machine  stops. 

2— Phys.  17 


18  CELLS. 

Still  another  comparison  may  be  drawn  between  the  body 
and  a  piece  of  machinery — say,  a  steam  engine.  There  is  for 
both  the  need  of  fuel  that  can  be  oxidized  by  burning,  and 
of  resultant  energy,  liberated  in  the  form  of  heat  and  visible 
motion.  Also,  as  the  parts  arc  subject  to  wear  and  tear,  new 
parts  must  be  supplied.  In  the  case  of  a  steam  engine,  the 
fuel  is  the  coal  fed  to  the  boiler  and  oxidized  by  burning.  In 
man  the  fuel  is  the  food  we  eat,  burned  up  in  the  presence  of 
the  oxygen  we  breathe.  But  here  the  analogy  ceases,  for 
whereas  the  coal  supplied  to  a  steam  boiler  never  forms  an 
integral  part  of  the  boiler,  in  man  the  food-stuffs  are  absorbed 
and  go  to  form  part  of  the  individual  himself  before  they  are 
broken  down  by  the  oxidizing  agent. 

Metabolism:  The  process  of  building  up  the  food-stuffs, 
already  properly  digested,  into  a  part  of  the  body  is  called 
anabolism.  The  breaking  down  is  the  kataboiie  process, 
or  katabolism.  Both  together  are  called  metabolism. 

To  make  the  simile  between  man  and  a  steam  boiler  perfect, 
we  should  have  to  imagine  a  boiler  made  of  coal,  instead  of 
iron,  which  being  ignited  on  its  inner  surface  generated  heat 
which  caused  the  contained  water  to  boil.  And  further,  we 
should  have  to  imagine  that  as  fast  as  the  inner  layers  of  coal 
were  consumed  fresh  coal  was  placed  on  the  outside  to  make 
up  for  the  loss. 

Thus  we  see  that  food  is  digested,  absorbed,  and  incor- 
porated into  the  body,  only  to  be  broken  down  again  by  oxi- 
dation. 

This  oxidation,  or  burning,  is  the  source  of  the  <//ov///  of 
the  body,  manifested  as  heat  and  visible  motion;  and  also  of 
certain  waste-products,  comparable  to  the  smoke  and  noxious 
gases  of  a  steam  boiler. 

These  waste-products  are  eliminated  by  the  body  through 
four  great  channels — the  breath,  sweat,  urine,  and  faeces. 

CELLS. 

General  structure :  The  fundamental  element  or  unit  of 
structure  of  all  living  bodies  is  the  cell.  Some  bodies,  for 
example  the  amoeba,  are  so  small  and  so  simple  in  structure 
as  to  consist  of  only  a  single  cell.  On  the  other  hand,  the 


ESSENTIAL  FEATURES  OF  A   CELL.  19 

higher  animals  have  millions  of  cells,  highly  differentiated 
for  the  different  functions  they  are  called  upon  to  perform. 
Let  us  examine  a  cell,  and  see  what  it  looks  like  and  of  what 
it  consists. 

A  cell  (Fig.  1)  is  a  mass  of  living  matter,  known  as  proto- 
plasm, varying  from  ^-oVo^h  to  T2"otn  °f  an  ^ncn  'n  diameter, 
which  may  or  may  not  have  a  limiting  membrane  or  capsule. 
As  a  general  rule,  animal  cells  do  not  have  a  capsule,  while 
vegetable  cells  usually  do.  The  contents  of  the  cells  may  be 
liquid,  semi-liquid,  or  granular  in  character.  The  granules 

FIG.  1. 


Buccal  and  glandular  epithelium. 

in  some  cells,  according  to  many  histologists,  are  united  by 
filaments,  the  cell-contents  consisting  then  of  a  network. 

The  nucleus:  Usually  amidst  the  cell-contents  may  be  seen 
a  still  smaller  cell,  the  nucleus  ;  and  within  this  the  nucleo- 
lus.  Though  in  some  kinds  of  cells  no  nucleus  can  be  found, 
it  may  be  assumed  as  true  that  at  some  period  of  its  life  every 
cell  had  one,  though  it  may  have  been  lost  in  the  course  of 
development. 

Essential  features  of  a  cell :  Great  difference  still  prevails 
among  histologists  as  to  the  relative  importance  of  the  nucleus 


20  CELLS. 

and  nucleolus;  of  the  cell-contents  and  cell-wall.  Some  hold 
that  the  nucleus  is  the  all-important  element  in  cell-life ; 
others  maintain  that  the  cell-contents  hold  this  position.  As 
yet  their  relative  significance  is  not  definitely  understood. 

Importance  of  the  cell :  Though  there  is  some  doubt  as  to 
the  exact  use  of  the  different  parts  of  the  cell,  no  doubt 
exists  that  the  life  of  the  organism  resides  in  the  cells  com- 
posing it.  Among  reasons  for  this  belief  may  be  mentioned 
the  fact  that  the  life  of  human  beings  begins  as  the  ovum,  a 
cell ;  and  that  the  tissues  of  the  embryo  consist  of  modified 
cells,  the  lineal  descendants  of  this  primitive  cell  or  ovum. 

Cells — gemmation:  If  one  watches  the  career  of  a  cell,  it 
will  be  seen  to  give  out  a  little  bud  or  sprout  from  one  side  ; 
this  bud  or  sprout  grows  in  size,  and  the  band  connecting  it 
with  the  original  mass  becomes  more  and  more  constricted 
until  the  offshoot  is  separated  from  the 
FIG.  2.  parent-mass.    Thus  a  new  cell  is  born, 

and  after  its  full  growth  is  attained  it 
shows  all  the  characteristics  of  the 
parent-cell.  Such  a  process  of  birth 
is  called  "  gemmation  "  (Fig.  2). 

Karyokinesis :  This  (Fig.  3)  is  the 
indirect  or  mitotic  division  of  the 
nucleus,  hence  also  called  karyomi- 
tosis.  The  cell-nucleus  is  enlarged, 
and  its  net-like  arrangement  dis- 
appears and  is  changed  into  a  skeiu  of 
filaments  of  chromoplasm,  into  which 
Divem°bryo0fof  slagl^ey).  In  the  uudeoli  are  merged  (convolution). 
Now  appears  another  set  of  filaments, 

arranged  like  a  spindle,  which  grows  until  equal  to  the  diam- 
eter of  the  nucleus.  By  this  time  the  filaments  of  the  first- 
named  skein  of  filaments  have  become  shorter  and  V-shaped, 
and  radiate  from  the  equator  of  the  spindle  (aster  stage). 
Then  each  chromoplasmic  filament  splits  longitudinally  into 
two  others,  and  separation,  beginning  at  the  V,  is  soon  distinct. 
The  apices  of  all  these  loops  of  filaments  now  swing  away  from 
the  equator  of  the  spindle  and  point  toward  the  poles  of  the 
spindle,  so  that  their  ends  look  toward  the  equator  (diaster 


DECAY  AND  DEATH  OF  CELLS. 


21 


stage).  There  are  thus  two  groups  of  filaments,  the  apices  of 
one  pointing  to  one  pole  and  those  of  the  other  group  pointing 
to  the  opposite  pole  of  the  spindle.  Each  group  becomes  con- 
verted into  a  daughter-nucleus,  and  the  process  is  completed 
by  a  complete  constriction  and  division  across  the  equator  of 


FIG.  3. 


Karyokinesis.  A,  ordinary  nucleus  or  a  columnar  epithelial  cell;  B,  c,  the  same 
nucleus  in  the  stage  of  convolution  ;  D,  the  wreath  or  rosette  form  ;  E,  the  aster 
or  single  star ;  p,  a  nuclear  spindle  from  Descemet's  endothelium  of  the  frog's 
cornea ;  G,  H,  i,  diaster ;  K,  two  daughter-nuclei  (Klein). 

the  spindle,  two  nuclei  being  thus  produced,  as  the  cell-pro- 
toplasm soon  divides  also. 

Development  of  cells  :  The  daughter-cells,  whether  produced 
by  the  direct  or  the  indirect  form  of  cell-division,  grow  until 
they  reach  maturity.  They  then  in  turn  subdivide  and  give 
origin  to  more  cells.  Thus  it  will  be  seen  that  every  cell 
owes  its  origin  to  some  preexisting  cell. 

As  to  the  question  of  the  origin  of  the  original  parent-cell 
f  all  living  matter,  we  have  no  answer.  The  whole  process 
f  cell-division  and  cell-structure  is  far  more  complex  than 
as  been  given  above ;  and  for  further  details  the  student  is 
referred  to  more  exhaustive  works  on  the  subject. 

Decay  and  death  of  cells  :  The  comparatively  brief  life  of 
cells  is  brought  to  an  end  either  through  mechanical  abrasion 
or  by  chemical  transformation.  Epithelial  cells  give  frequent 


; 


22  CELLS. 

examples  of  the  former  method.  As  the  coll  approaches  the 
surface  it  becomes  more  and  more  flattened  and  scaly,  till  tit 
last  it  is  simply  rubbed  off.  Hence  epithelial  cells  are  found 
in  the  mucus  of  the  mouth,  intestine,  etc.  In  the  case  of 
chemical  transformation  the  cell  degenerates  in  various  ways, 
the  process  being  frequently  normal,  though  it  may  1><-  patho- 
logical. Thus  fatty  degeneration  of  the  cells  in  the  breast 
produces  the  oil-globules  in  the  secretion  of  milk. 

The  protoplasm  of  which  all  cells  are  made  up  has  been 
called  the  basis  of  life.  Protoplasm  is  an  unstable  albuminoid 
substance  of  more  or  less  gelatinous  consistency.  Its  reactions 
are  those  of  albumin  (coagulation  by  heat  and  mineral  acids), 
and  its  chemical  composition  is  in  varying  proportions  of  the 
elements  C,  H,  O,  N,  and  S.  Protoplasm  is  living  albumin, 
or  proteid.  Besides  proteid,  every  cell  contains  water. 

The  amoeba  is  a  microscopic  animal  that  consists  of  but 
one  cell ;  yet  this  one  cell  performs  all  the  animal  functions. 

FIG.  4. 


Protamoeba  (Haeckel). 


(1)  It  is  capable  of  motion  (Fig.  4),  the  cell  sending  out  a 
small   branch  or  arm  of  the   protoplasm.     This   branch,  or 
pseudopod  as  it  is  called,  attaches  itself  to  some  part ^  of  the 
environment,  and  then  the  rest  of  the  cell  is  drawn  forward 
until  the  whole  cell  seems  to  flow  to  and  into  its  branch.     The 
process  is  then  repeated,  the  cell  advancing  steadily  forward. 

(2)  It  has  the  power  of  food-absorption  ;  the  cell  flowing 
around  and  completely  enveloping  any  particle  of  food  it  may 
meet,     Later  on,  such  of  the  rood  as  has  not  been  absorbed  is 
excreted,  by  a  process  of  flowing  away,  on   the  part  of  the 
protoplasm. 


EPITHELIUM.  23 

(3)  It  also  absorbs  oxygen  from   the  surrounding   atmos- 
phere. 

(4)  It  is  irritable  to  stimuli;  and  is  capable  of  (5)  repro- 
duction and  (6)  growth. 

Thus  we  see  that  the  amoeba  presents  in  its  single  cell  all 
the  main  functions  of  the  higher  animals.  But  the  individual 
cells  of  the  human  body  are  by  no  means  so  well  endowed 
with  functions  as  the  amoaba. 

Differences  between  plants  and  animals :  The  most  essential 
difference  lies  in  the  fact  that  vegetable  protoplasm  can  build 
up  new  albuminous  compounds  out  of  such  chemical  bodies 
as  water,  carbonic  acid  gas,  and  inorganic  mineral  salts. 
Animal  protoplasm,  on  the  other  hand,  must  have  ready- 
formed  albuminous  food  in  order  to  live.  Vegetables  exhale 
oxygen,  but  inhale  carbonic  acid  gas ;  while  animals  do  the 
reverse. 

Specialization  of  cells :  As  a  rule  the  body-cells  are  highly 
specialized  for  the  fulfilment  of  one  or  more  functions,  to  the 
exclusion  of  all  others.  Where  we  find  two  or  more  cells  of 
the  same  kind  aggregated  together,  the  mass  is  called  a  tissue. 

Two  or  more  tissues  of  different  kinds  are  spoken  of  as 
organs. 

By  apparatus  is  meant  an  association  of  organs  for  the  per- 
formance of  a  common  function.  Thus  the  stomach,  intes- 
tines, and  pancreas  may  be  spoken  of  as  a  collection  of  organs, 
forming  an  apparatus  for  the  common  function  of  digestion. 

In  ordinary  parlance  an  organ  is  "  the  instrument  of  func- 
tion, the  performer  of  a  function." 

Classification  of  tissues:  The  cells  in  man  are,  roughly 
speaking,  found  to  make  four  main  classes  of  tissues :  epithe- 
lial, connective-tissue,  blood-cells,  and  nerve-cells. 

Epithelium :  The  name  "  epithelium  "  is  given  to  the  cells 
which  cover  the  skin,  and  the  mucous  and  serous  membranes 
)f  the  body ;  and  which  also  enter  into  the  formation  of  the 
;lands.  Its  varieties  are — (1)  simple,  a  layer  of  flat  (squarn- 
>us),  cubical  (spheroidal),  or  cylindrical  (columnar)  cells,  as 
in  the  serous  and  mucous  surfaces ;  (2)  stratified,  when  it 
occurs  in  layers,  as  in  the  skin ;  (3)  transitional,  where  it  has 
the  characteristics  of  both  in  situations  where  the  other  two 


24 


CHEMISTRY  OF  THE  BODY. 


FIG.  5. 


forms  approach  one  another,  as  in  the  bladder.  (4)  In  the 
"•lands  are  (\n\i\d  functional  cell*,  which  partake  of  the  charac- 
ter of  the  epithelium  of  the  surface.  They  are  arranged  in 
groups  about  the  ducts.  Such  cells  are  often  known  as 
secreting  or  glandular  epithelial  cells. 

Simple  epithelium  possesses  hair-like  processes  in  certain 
locations,  and  this  is  known  as  viliutctl  epithelium  (Fig.  5). 
The  hairs  are  endowed  with  motion,  and 
wave  in  such  a  manner  as  to  throw  for- 
ward small  particles  which  fall  upon 
them. 

The  principal  uses  of  epithelium  are: 
protection,  as  skin,  serous  surfaces; 
motion,  ciliated  epithelium  of  air-pas- 
sages and  Fallopian  tubes  ;  secretion,  in 
glands — e.  </.,  gastric  juice;  sensation, 
in  the  cones  of  the  retina,  olfactory 
cells  of  the  nose,  etc. 

Endothelium  is  a  simple  form  of 
squamous  or  scale-like,  flat  epithelial 
cells  which  line  the  serous  membranes  and  the  bloodvessels. 
The  cells  arc  very  delicate,  and  are  not  stratified.  They  are 
of  various  forms,  usually  irregularly  polygonal,  and  are 
joined  at  the  edges  so  as  to  form  a  sort  of  mosaic. 

Connective  tissues  form  the  frame  and  supports  of  the  body 
and  of  the  organs  of  the  body.  The  ligaments,  tendons, 
fasciae,  cartilages,  and  bones  are  examples  of  them.  The 
fibrous  connective-tissue  cells  are  found  in  all  organs  in 
greater  or  less  amount.  In  the  organs  whose  use  is  the  sup- 
port of  the  body  or  one  of  its  members  these  cells  predomi- 
nate. In  other  organs  the  fibrous  cells  serve  to  hold  in  place 
the  functional  cells  and  to  maintain  the  shape  of  the  organs. 


Columnar  ciliated  epithe- 
lium-cells, from  the 
human  nasal  membrane ; 
magnified  300  diameters 
(Quain  and  Sharpey).  - 


CHEMISTRY  OF  THE  BODY. 

The  ultimate  analysis  of  the  human  body  shows  it  to  con- 
sist of  the  following  elements:  carbon,  hydrogen,  oxygen, 
nitrogen,  magnesium,  calcium,  sodium,  potassium,  sulphur, 
phosphorus,  manganese,  silica,  iron,  chlorine,  fluorine,  and 


PROXIMATE  PRINCIPLES.  25 

iodine.  Of  these,  only  oxygen  and  nitrogen  are  found  free, 
the  other  elements  existing  as  compounds. 

By  proximate  principles  we  mean  those  elements  or  com- 
pounds that  exist  as  such  in  the  body.  Thus  sodium  chloride 
is  a  proximate  principle,  as  it  is  found  as  such  in  the  human 
body.  Neither  the  metal  sodium  nor  the  gas  chlorine,  how- 
ever, can  be  considered  as  belonging  to  this  class,  as  they  do 
not  exist  or  act  as  such  in  the  body.  The  proximate  princi- 
ples are  subdivided  into  two  great  classes — organic  and 
inorganic.  It  will  be  wise  to  attempt  at  this  point  to 
draw  a  clear  distinction  bet\veen  organic  and  inorganic  sub- 
stances. 

Organic  substances  are  nearly  always  highly  complex  bodies 
containing  many  elements.  Two  particular  elements — carbon 
and  hydrogen — enter  into  all  organic  bodies.  Some  organic 
substances  are  very  simple  chemically  and  may  contain  no 
elements  except  carbon  and  hydrogen.  It  was  formerly 
supposed  that  any  substance  must,  in  order  to  be  included  in 
this  class,  have  been  at  some  time  either  an  intimate  part  of, 
or  a  product  of  the  activity  of,  a  living  body ;  or  else  either 
an  intimate  part  of,  or  a  product  of  the  decomposition  of,  a 
body  that  had  lived.  Of  recent  years,  however,  many  of 
these  principles  have  been  prepared  in  the  laboratory  from 
inorganic  elements  without  invoking  the  aid  of  a  so-called 
"  vital  force  "  ;  and  there  is  every  reason  to  suppose  that  in 
time  all  will  be.  Such  being  the  case,  the  distinction  between 
organic  and  inorganic  substances  regarded  at  one  time  as  being 
so  essential,  is  without  philosophical  significance,  and  is  only 
made  use  of  as  a  matter  of  convenience.  Organic  substances 
are  further  subdivided  into  those  containing  nitrogen  and 
those  not  containing  it. 

Inorganic  substances  are  best  defined  by  negativing  the 
above  conditions — that  is  to  say,  if  a  chemical  body  fails  to 
fulfil  every  condition  given  above,  it  cannot  be  classed  as 
"organic,"  but  is  u  inorganic."  Carbon  dioxide  (CO2)  is  a 
body  that  fulfils  all  the  conditions  for  being  organic  to  a  marked 
degree,  except  that  there  is  no  hydrogen  present ;  hence 
breaking  the  rule  that  both  carbon  and  hydrogen  must  be 
present  in  order  that  a  body  be  organic.  Nevertheless  carbon 


26  CHEMISTRY  OF  THE  BODY. 

dioxide  is  the  one  exception  allowed,  and  is  classed  among 
both  organic  and  inorganic  substances. 

With  few  exceptions  the  inorganic  principles  are  so  firmly 
combined  with  the  organic  that,  as  the  latter  become  effete 
and  are  eliminated,  the  inorganic  substances  are  cast  out  with 
them.  Some  of  them  play  a  more  important  role  than  others 
and  are  found  in  greater  quantities. 

List  of  inorganic  proximate  principles :  The  inorganic  prin- 
ciples found  in  the  human  body  are:  oxygen;  nitrogen; 
water  ;  hydrochloric  acid  ;  chlorides  of  sodium  and  potassium  ; 
sulphates  of  sodium  and  potassium  ;  carbonates  of  sodium, 
potassium,  calcium,  and  magnesium  ;  phosphates  of  sodium, 
potassium,  calcium,  and  magnesium;  also  small  amounts  of 
compounds  containing  iron,  silica,  fluorine,  iodine,  and  man- 
ganese. To  complete  the  list  we  must  add  carbon  dioxide. 

Uses  of  inorganic  proximate  principles:  The  uses  to  which 
these  principles  are  put  by  the  body  are  not  well  understood  ; 
but  they  are  necessary  in  making  the  structure  of  the  body  or 
in  aiding  chemical  work.  They  are  not  sources  of  chemical 
potential  energy.  Many  of  the  inorganic  proximate  principles 
are  taken  into  the  body  and  excreted  unchanged.  Others 
not  only  are  taken  into  the  body,  but  are  also  manufactured 
in  the  body  as  the  result  of  oxidation  and  breaking  up  of 
more  complex  organic  bodies.  As  a  result  of  this  manu- 
facture we  should  expect  to  find  that  certain  of  the  inorganic 
proximate  principles  are  excreted  in  greater  amounts  than 
they  are  ingested.  Such  is  proven  to  be  the  case,  for  water, 
and  the  sulphates,  phosphates,  and  carbonates  leave  the  body 
in  greater  amount  than  that  in  which  they  enter. 

Distribution:  The  inorganic  proximate  principles  are  found 
distributed  in  various  parts  of  the  body.  Water  and  sodium 
chloride  are  omnipresent.  Oxygen  and  nitrogen  are  found  in 
the  blood  and  tissues.  Potassium  chloride  is  found  generally, 
but  not  so  omnipresent  as  the  chloride  of  sodium.  The  phos- 
phates and  the  carbonates  of  the  alkaline  metals  are  found  in 
the  blood,  rendering  the  latter  alkaline.  The  phosphates  and 
carbonates  of  the  alkaline  earths  are  neutral,  and  give  rigidity 
to  the  bones.  Hydrochloric  acid  is  present  in  the  gastric 
juice.  The  less  important  salts  are  found  elsewhere,  and 


PROXIMATE  PRINCIPLES.  27 

play  but  an  insignificant  part.     Water  constitutes  more  than 
two-thirds  of  the  weight  of  the  body. 

Organic  proximate  principles  are  divided  into  two  great 
classes  :  (1)  nitrogenous  and  (2)  non-nitrogenous. 

(1)  The  former  take  the  principal  part  in  the  formation  of 
the  solid  constituents  of  the  body,  and  occur  in  all  the  body- 
tissues  and  -fluids.     They  make  up  the  protoplasm  of  cells 
and  essential  ingredients  of  the  fluids,  both  circulatory  and 
excretory.     Chemically,  they  are  compounds  of  C,  H,  O,  N, 
sometimes  with    sulphur  or  phosphorus.     These,  with   few 
exceptions,  are  not  crystallizable. 

(2)  The  latter  (non-nitrogenous)  class  of  bodies  are  made 
up  of  the  fats  and  carbohydrates.     With   the  exception  of 
starch,  all  of  this  class  are  crystallizable. 

In  striking  contrast  with  the  inorganic  proximate  princi- 
ples, none  of  those  belonging  to  the  organic  division,  with  the 
exception  of  butter  and  sugar  of  milk  among  the  non-nitrog- 
enous ;  and  of  casein  of  milk,  mucus,  epithelium,  and  epider- 
mis, among  the  nitrogenous  principles,  ever  appear  among 
the  excretions  or  secretions  of  the  healthy  human  body. 

Uses  of  organic  proximate  principles :  All  our  vital  manifes- 
tations depend  on  the  energy  derived  from  the  organic  matter 
of  the  body.  This  organic  matter  is  constantly  being  used 
up,  and  to  supply  its  place  the  body  must  acquire  fresh  organic 
matter.  The  essence  of  life  is  in  change,  and  in  this  change 
the  element  nitrogen  plays  a  very  important  part  because  of 
the  readiness  with  which  the  nitrogenized  proximate  princi- 
ples break  down.  This  liability  to  breaking  down  is  not  only 
due  to  the  presence  of  nitrogen,  but  also  to  the  great  number 
of  molecules  which  all  organic  principles  contain.  Through 
this  breaking  down  is  derived  the  energy  required  for  life. 

Source  of  organic  supply:  Green  plants  have  the  power,  by 
virtue  of  the  chlorophyl  in  their  substance,  to  convert  the  in- 
organic compounds,  that  are  the  food  for  plants,  into  simple 
organic  bodies.  Animals,  on  the  other  hand,  cannot  convert 
their  inorganic  foods  into  organic  substances,  but  are  com- 
pelled to  eat  organic  bodies  in  order  to  have  the  necessary 
fuel  on  which  they  live.  To  illustrate  :  green  plants  live  on 
water,  nitrite  and  nitrate  of  potassium,  sulphates  of  calcium 


28 


CHEMISTRY  OF  THE  BODY. 


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3.  Derived  albumins,  derived 
from  Class  1  by  action  of 
acids,  alkalies,  or  ferments. 
4.  Fibrin,  from  Class  1  by  ac- 
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heat,  etc.,  from  Class  1, 

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PROXIMATE   PRINCIPLES. 


29 


ORGANIC  BOD] 

3  PRINCIPLES. 

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30  THE  BLOOD. 

and  magnesium,  the  phosphates  of  calcium,  and  some  soluble 
salts  of  iron,  all  of  which  exist  in  the  earth  ;  also  on  the 
oxygen  and  carbon  dioxide  of  the  air.  By  various  chemical 
combinations  and  changes  these  inorganic  compounds  are  con- 
verted by  the  green  plant  under  the  influence  of  sunlight  into 
simple  organic  substances. 

Non-chLorophyl-bearinfj  plants,  such  as  fungi,  have  not  the 
property  of  absorbing  inorganic  substances  and  converting 
them  into  organic  substances,  but  must  receive  their  food 
in  the  form  of  organic  compounds;  hence  the  fungi  live  on 
other  plants.  So  too  with  animals  ;  they  must  live  on  plants 
and  other  animals.  From  these  plants  and  animals  we  cat 
we  obtain,  besides  a  number  of  inorganic  salts,  water,  etc., 
the  three  great  classes  of  food-stuffs  which  are  eventually  to  be 
digested,  altered,  and  assimilated  into  the  body,  then  "  burned  " 
with  the  liberation  of  energy,  and  finally  to  be  cast  off  as 
waste-products  by  means  of  the  sweat,  breath,  urine,  and 
faeces.  These  three  classes  of  food-stuffs  are  protei^,  c<ti-l><>- 
hydrates,  and  fats.  How  these  foods  are  absorbed  and  assim- 
ilated will  be  studied  later  in  the  chapter  on  Digestion.  To 
be  sources  of  energy,  the  tissues  of  the  body  must  be  oxidized  ; 
this  is  accomplished  by  the  oxygen  conveyed  from  the  lungs 
to  the  tissues  by  the  blood. 

THE  BLOOD. 

General  observations :  Since  the  earliest  times  it  has  been 
recognized  that  the  blood  is  the  most  important  fluid  in  the 
human  body ;  that  it  is,  indeed,  indispensable  to  life.  Its 
loss  prostrates  and  enfeebles  the  body.  With  excessive 
hemorrhage  life  itself  ebbs  away.  This  is  readily  evident 
when  it  is  known  that  the  blood,  circulating  through  the  sys- 
tem, carries  to  the  tissues  and  the  cells  composing  them 
material  for  their  growth,  renewal,  and  repair;  and  removes 
from  them  that  which  has  become  effete.  It  also  tends  to 
equalize  more  or  less  the  temperature  throughout  the  body. 

Gross  appearance:  Freshly  drawn  blood  is  a  somesvhat 
viscid  opaque  fluid  of  a  more  or  less  pronounced  red  color. 
This  color,  which  depends  entirely  on  the  amount  of  oxygen 
present  in  the  blood,  varies  according  as  the  blood  is  drawn 


PHYSICAL   CHARACTERISTICS. 


31 


from  the  arterial  or  the  venous  system.  That  drawn  from 
the  arteries  or  pulmonary  veins  is  of  a  bright  scarlet,  and 
contains  a  large  amount  of  oxygen  ;  while  that  from  the 
systemic  veins  is  bluish-red  to  reddish- black,  and  has  far 
less  oxygen.  The  opacity  is  due  to  the  fact  that  blood  is  not 
a  homogeneous  liquid,  but  consists,  as  we  shall  see  later,  of 
two  elements — corpuscles  and  plasma.  These,  differing  in 
their  refractive  power,  oppose  the  transmission  of  light,  thus 
causing  the  opacity. 

FIG.  6. 


Human  blood  as  seen  on  the  warm  stage.  Magnified  about  1000  diameters,  c,  c, 
crenated  red  corpuscles;  p,  a  finely  granular ;  g,  a  coarsely  granular  pale  cor- 
puscle ;  both  exhibit  two  or  three  vacuoles.  In  g  &  nucleus  also  is  visible. 
r,  r,  single  red  corpuscles,  flat;  r',  r',  the  same  on  edge;  r",  r",  the  same  in 
rouleaux  (Quain). 

Physical  characteristics :  The  specific  gravity  of  the  blood 
at  ordinary  temperature  varies  between  1045  and  1062.  It 
is  of  a  slightly  alkaline  reaction,  due  to  the  phosphates  and 
carbonates  of  the  alkaline  metals,  and  has  a  salty  taste  and  a 
peculiar  characteristic  odor.  The  degree  of  alkalinity,  esti- 
mated as  Na,CO3,  corresponds  in  human  blood  to  0.35  per 
cent,  of  this  salt. 


32 


THE  BLOOD. 


If  examined  under  the  microscope,  the  blood  will  be  seen  to 
consist  of  a  fluid,  called  plasma  or  liquor  sanguinis,  in  which 
are  suspended  small  particles  called  blood-corpuscles.  The 
corpuscles  are  of  three  types,  known  as  red  corpuscles,  white 
corpuscles  or  leukocytes,  and  blood-plates  or  microcytcx. 

The  temperature  of  the  blood  in  man  is,  on  the  average, 
98.9°  F. ;  but  it  is  very  probable  that  in  certain  parts  of  the 
body  it  is  several  degrees  higher. 

Quantity  of  blood :  The  total  amount  of  blood  is  estimated 
as  being  one- thirteenth  of  the  body-weight.  Thus  in  an  in- 
dividual weighing  one  hundred  and  seventy  pounds,  the 

FIG.  7. 


Red  globules  of  the  blood,  seen  a  little  beyond  the  focus  of  the  microscope  (Dalton). 

amount  of  blood  in  his  body  would  weigh  about  thirteen 
pounds  and  would  measure  about  six  quarts.  The  corpuscle* 
weigh  about  one-third  of  the  total  blood- weight. 

Corpuscles  :  The  corpuscles  (Fig.  6)  exist  in  large  numbers 
in  the  blood,  it  being  estimated  that  in  every  cubic  millimetre1 
of  blood  there  are  10,000  leukocytes,  250,000  blood-plates, 
and  5,000,000  red  corpuscles. 

Red  corpuscles:  Human  colored  blood-corpuscles  (Figs. 
7  and  8)  are  circular,  biconcave  disks  with  rounded  edp-  :  in 


RED   CORPUSCLES. 


33 


diameter  they  are  about  s^nj-th  in. ;  in  thickness  about 
in.  In  water  they  swell  and  become  flat  or  convex.  When 
seen  singly  they  appear  yellow,  but  their  color  is  red  when 
seen  in  groups.  Microscopic  examination  shows  that  they 
have  no  nucleus  and  no  limiting  membrane ;  but  they  have 
an  elastic  framework,  or  stroma,  which  retains  an  individ- 


FIG. 


Red  globules  of  the  blood,  seen  a  little  within  the  focus  (Dalton). 

uality  for  each  corpuscle,  and  allows  changes  of  shape  to  adapt 
them  for  capillary  circulation,  and  brings  them  back  to  the 
original  form  after  such  distortion. 

The  color  is  due  to  a  chemical  body,  called  haemoglobin, 
which  is  held  within  the  stroma.  The  red  corpuscles  have  a 
specific  gravity  of  1088,  and  are  the  heaviest  of  the  compo- 
nent parts  of  the  blood. 

In  all  mammals,  with  the  exception  of  the  camel  family, 
the  c/encrdl  character  of  the  corpuscles  is  the  same  as  in  man ; 
but  their  size  varies  in  the  different  animals  (Fig.  9).  The 
camel  family  have  the  same  corpuscles  as  other  mammals, 
except  that  the  discs  are  oval  instead  of  circular. 

In  reptiles,  fishes  (except  a  few  species),  and  birds  the  red 
corpuscles  are  oval,  nucleated,  and  usually  larger  than  those 
of  mammals. 


34  THE  BLOOD. 

Red  corpuscles — origin  :   Like  all  the  other  cellular  elements 
of  the  body,  there  must  be  a  birth  of  new  blood-cells  to  take 


Mainnjiils.     Birds.        Reptiles. 


Amphibia. 


the  place  of  those  whose  life-work  is  done.     The  ancestors 
of  the  red  blood-corpuscles  are  the  large,  irregular,  polyn-«>- 


RED   CORPUSCLES.  35 

nal  marrow-cells.  These  marrow-cells  are  found,  as  their 
name  implies,  in  the  marrow  of  the  long  bones.  They  are 
found  in  layers  or  phalanxes,  each  phalanx  a  little  more 
highly  developed  than  the  layer  underlying  it.  The  most 
highly  developed  divide  by  karyokinesis,  and  are  pushed  oif 
from  the  mass  of  cells  by  the  growth  of  the  cells  below.  The 
detached  cells,  after  undergoing  certain  changes  in  shape,  enter 
the  blood-current  and  become  the  ordinary  red  blood-corpus- 
cle. The  marrow-cell  is  polygonal,  nucleated,  and  only  very 
slightly  colored.  To  become  a  red  blood-cell  the  marrow- 
cell  loses  its  nucleus,  assumes  the  biconcave  disc-shape,  and 
acquires  a  greater  amount  of  coloring-matter,  or  haemoglobin. 
Such  changes  have  been  observed  to  take  place  in  the  mar- 
row-cells; and  also  in  cases  in  which  individuals  have  suf- 
fered severely  from  hemorrhage,  during  the  recuperation, 
numbers  of  only  partially  transformed  marrow-cells  have 
been  found  circulating  in  the  blood-current,  not  having  had 
time  to  be  fully  altered,  as  the  demand  for  new  cells  was  so 
urgent. 

What  becomes  of  the  nuclei  which  the  marrow-cells  cast 
oif  is  not  known.  Suggestions  have  been  made  that  these 
nuclei  may  become  the  blood-plates  or  else  be  destroyed  by 
the  leukocytes.  These  are  merely  suggestions,  and  not  to  be 
accepted  as  proven.  Where  the  increase  in  coloring-matter 
which  the  marrow-cell  acquires  comes  from,  is  also  a  source 
of  speculation. 

Red  corpuscles — function:  The  one  important  and  funda- 
mental purpose  of  the  red  blood-corpuscles  is  to  convey 
o.i't/f/cii.  from  the  lungs  to  the  tissues.  As  has  been  said,  the 
red  corpuscles  consist  of  an  elastic  network  or  stroma,  which 
holds,  probably  both  mechanically  and  chemically,  a  highly 
complex  protcid  body  called  haemoglobin,  which,  although 
cry  stall  izable,  is  non-diffusible.  The  form  of  the  crystals 
of  haemoglobin  varies  in  different  animals.  In  man  they  are 
prismatic,  in  the  guinea-pig  they  are  tetrahedral,  in  the 
squirrel  they  are  hexagonal,  and  so  on. 

Hamoglobin  can  be  subdivided  into  two  bodies— globulin 
(96  per  cent.)  and  hsematin  (4  per  cent.). 

Hcemin  (Fig.  10),  the  hydrochlorate  of  haematin,  is  formed 


36 


THE  BLOOD. 


by  adding  muriatic  acid  to  haemoglobin.  It  is  of  especial 
iui.  rest  from  u  medico-legal  point  of  view,  as  it  can  be 
obtained,  by  proper  manipulation,  from  a  very  minute 
<juantity  of  blood.  It  forms  characteristic  crystals,  rhombic 


Fio.  10. 


Rhombic  crystals  of  hsemin,  or  hydrochlorate  of  haematiu. 

tablets,  which  are  sometimes  disposed  as  stars  or  crosses, 
of  a  red  or  brown  color.  If  oxygen  be  added,  the  crystals 
assume  a  violet  hue,  while  under  the  influence  of  carbon 
dioxide  the  crystals  lose  their  transparency.  Unfortunately, 
however,  (here  is  no  characteristic  form  of  these  crystals  for 
the  different  animals.  We  can  prove  that  a  certain  material 
is  or  is  not  blood,  but  not  that  it  is  or  is  not  human  blood. 

Globulin  is  composed  of  the  elements  C,  H,  N,  O,  and  S. 
Ihriiuifin  is  composed  of  the  elements  C,  H,  N,  O,  and  Fe. 
The  iron  \<  the  important  element;  for  the  oxygen  from  the 
lungs  forms  a  very  loose  chemical  combination  with  the 
iron  in  the  haemoglobin. 

When  the  red  corpuscle  rich  in  haemoglobin  reaches  the 
lungs  the  oxygen  absorbed  from  the  air  is  rapidly  taken  up 
in  lo<»-c  chemical  combination  by  the  haemoglobin.  The 
corpuscle  is  now  hurried  with  it.-  load  of  oxygen  to  the  dis- 


RED   CORPUSCLES. 


37 


tant  tissues,  where  the  oxygen  is  absorbed  by  the  tissues,  and 
the  red  corpuscle  is  carried  back  to  the  lungs  for  a  fresh 
supply.  Besides  this,  the  red  corpuscle  has  no  other  func- 
tion except  diapedesis — i.  e.,  a  passive  ability  to  pass  through 
capillary  walls.  The  student  must  bear  in  mind  that  the 
oxygen  which  enters  into  the  chemical  compound  called 


Red.     Orauge.  Yellow.        G 


O xy haemoglobin  and 
NO2-haemoglobin. 


CO-hsemoglobin. 


Reduced  haemoglobin. 


Hsematin  in  acid  solu- 
tion. 


Haematin  in  alkaline 
solution. 


Reduced  hsematin. 


Solar  spectrum  with 
Fraunhofer's  lines. 


haemoglobin  (see  formula  above)  is  not  the  oxygen  which 
unites  with  the  iron,  and  which  is  taken  into  the  hsemoglobin- 
molecule  in  the  lungs,  only  to  be  given  up  in  the  tissues. 
The  first  "  oxygen  "  spoken  of  is  an  essential  of  the  haemo- 
globin, and  is  retained  as  long  as  the  molecule  retains  its 
chemical  identity.  Haemoglobin  rich  with  the  oxygen  of 
respiration  is  called  oxyhcemoglobin.  When  this  oxygen  is 
entirely  removed  the  proteid  is  called  reduced  hemoglobin. 
Both  reduced  haemoglobin  and  oxyhaemoglobin  give  perfectly 


38  THE  BLOOD. 

characteristic  spectra  (Fig.  11).  This  point  has  been  of  some 
value  in  medico-legal  cases  in  determining  the  presence  of 
blood  in  suspected  stains. 

Red  corpuscles — death :  After  a  period  of  functional  activity 
the  red  blood-cell  has  outlived  its  utility  and  dies.  Other 
red  cell-  are  lost  from  the  circulation  by  hemorrhages  of  all 
kinds.  These  dead  and  lost  red  corpuscles  are  replaced 
by  new  cells  from  the  bone-marrow,  as  has  been  already 
shown.  Just  what  conditions  determine  the  death  of  a  red 
corpuscle,  or  just  how  the  dead  body  is  disposed  of,  is  not 
accurately  determined.  The  evidence  points  toward  the 
assumption  that  the  stroma  of  the  corpuscle  is  chemically 
destroyed  and  absorbed  by  the  tissues  as  proteid  material. 
The  haemoglobin,  after  the  destruction  of  the  framework,  is 
liberated  and  eventually  eliminated  as  a  part  of  the  bile- 
pigment. 

Leukocytes,  or  white  blood-corpuscles,  are  spherical,  granular 
masses  of  protoplasm,  each  having  a  nucleus,  but  no  cell- 
walls.  They  are  about  Y^Virtn  ll}-  *n  diameter.  Some  appear 
to  be  much  smaller,  and  probably  this  diminution  in  size  is  he- 
cause  these  corpuscles  have  not  yet  attained  full  development. 
It  has  been  said  above  that  the  leukocytes  are  spherical. 
This  is  true  when  the  leukocytes  are  being  carried  along  by  the 
blood-current ;  but  when  the  leukocytes  exercise  their  power 
of  locomotion,  which  permits  them  to  emigrate  (^igration) 
from  the  blood-current  into  the  surrounding  tissues,  each 
leukocyte  changes  its  shape  and  behaves  in  a  manner  iden- 
tical with  that  of  the  amoeba  (Fig.  12).  The  properties  and 
animal  functions  of  leukocytes  are  the  same  as  those  of  the 
amoeba. 

The  white  corpuscles  differ  in  many  respects,  other  than 
H/e  and  appearance,  from  the  red  ones.  They  are  differently 
affected  by  the  various  reagents.  They  keep  close  to  and 
even  seem  to  adhere  to  the  walls  of  the  vessels  in  which  they 
are  circulating,  while  the  red  corpuscles  keep  in  the  middle  of 
the  stream.  The  white  corpuscles  arc  found  in  lymph, chyle, 
pus  and  other  fluids  as  well  as  in  the  blood;  the  more 
general  name  of  leukocytes  is  often,  therefore,  given  to 
them. 


LEUKOCYTES. 


39 


Leukocytes — varieties  :  Three  varieties  of  leukocytes  have 
been  noted  in  the  blood.  The  most  marked  physical  differ- 
ence is  in  the  nuclei.  The  properties  are  the  same,  except 
in  the  amount  of  amoeboid  movement  exhibited. 

1.  Lymphocytes,  large  single  nucleus,  very  little  cytoplasm, 
practically  no  amoeboid  movement.     Most  commonly  found 
in  the  lymph. 

2.  Mononuclear    leukocytes,   large    corpuscles   with   single 
nucleus,   relatively  small  to  size  of  the  cell,  free  amoeboid 
movement. 

3.  Poly  nuclear  leukocytes  are  large  corpuscles  with  a  par- 
tially divided  nucleus  or  even  several  distinct  nuclei.     The 
amoeboid  movement  is  particularly  well  marked. 

FIG.  12. 


Various  forms  assumed  by  the  white  corpuscles  of  the  blood.  The  upper  row  repre- 
sents the  white  corpuscles  of  man  :  the  lower  row,  white  corpuscles  from  the 
newt,  showing  changes  effected  in  fifteen  minutes  (Carpenter). 

Undoubtedly  these  three  types  are  merely  three  stages  in 
the  development,  the  lymphocytes  being  the  youngest. 

Leukocytes — chemical  composition  :  Leukocytes  consist  of 
water,  inorganic  salts  (largely  potassium  salts),  proteids, 
glycogen,  nuclein,  fat,  lecithin,  cerebrin,  cholesterin. 

Origin :  The  leukocyte  owes  its  origin  to  the  splitting  up 
by  karyokinesis  of  some  previous  leukocyte  into  two  second- 
ary cells.  This  birth  takes  place  in  most  instances  in  the 


40  THE  BLOOD. 

lymphatic  or  adenoid  tissue,  and  the  new  cells  are  poured  into 
the  blood-current  by  lymphatic  channels. 

Function  :  Leukocytes  act  as  protecting  agents  for  the  body, 
by  destroying  bacteria  that  may  get  into  the  blood-current, 
lymph-  or  tissue-spaces  into  which  the  leukocyte  can  enter. 
The  method  of  destroying  the  bacteria  is  supposed  to  he 
either  by  a  process  in  which  the  leukocyte  ing<  MS  the  bac- 
terium (phagocytosis),  or  else  the  leukocyte  surrounds  the 
bacterium  with  some  substance  that  destroys  it.  The  leuko- 
cytes act  as  agents  in  assisting  the  absorption  of  flits  and  pep- 
tones from  the  intestines. 

Leukocytes  are  poured  out  in  large  numbers  in  any  wound 
in  the  body,  and  by  their  presence  act  as  barriers  to  infection. 
In  such  a  wound  some  of  the  leukocytes  may  eventually  be- 
come converted  into  granulation-tissue. 

Among  other  uses,  it  has  been  suggested  that  leukocytes, 
when  disintegrated,  help  keep  up  the  necessary  amount  of  pro- 
teid  in  the  blood-plasma. 

Death:  The  natural  ending  for  the  leukocyte  is  to  be  divided 
into  two  daughter-cells  by  karyokinesis.  Other  leukocytes 
are  disintegrated  in  the  blood-current.  Again,  other  leuko- 
cytes are  destroyed  in  the  battle  waged  against  bacteria. 
Others  are  lost  by  hemorrhage.  Still  others  may  be  con- 
verted into  granulation-tissue  in  wounds. 

Blood-plates :  The  blood-plates,  or  miarocytes,  are  small 
rounded  masses  of  which  little  is  known.  They  arc  much 
smaller  than  the  red  corpuscles.  The  blood-plates  arc  sup- 
posed to  assist  in  the  coagulation  of  blood  ;  but  all  we  know 
at  present  is  that  the  fibrin-fibrillae  seem  to  start  from  the 
microcytes.  The  microcytes  may  be  the  source  of  the  fibrin, 
or  may  merely  serve  as  mechanical  anchors. 

Blood-plasma:  The  flu  id  portion  of  the  blood  in  which  the 
corpuscles  float  is  called  plasma.  The  corpuscles  can  be  fil- 
tered out  under  certain  conditions,  leaving  the  plasma  f»r 
further  examination.  The  chief  method  is  by  filtration  at 
a  temperature  of  0°  to  3°  C. ;  but  equally  tr<»><l  results  may 
be  obtained  by  the  addition  to  the  blood  of  neutral  salts  in 
certain  proportions,  or  by  the  use  of  the  centrifugal  machine. 
It  differs  from  the  serum  in  containing  fibrinogen,  but  closely 


CHEMICAL  COMPOSITION  OF  BLOOD-PLASMA.        41 

resembles  that  fluid  in  reaction  and  appearance,  its  alkalinity, 
however,  being  somewhat  less. 

Blood-serum  :  The  serum  is  the  liquid  part  of  the  blood 
left  after  the  separation  of  the  clot.  It  is  alkaline,  trans- 
parent, of  a  yellow  color,  and  of  a  specific  gravity  of  about 
1030.  During  the  ordinary  process  of  coagulation  part  of 
the  serum  remains  in  the  clot  and  the  rest  is  squeezed  out. 
As  the  clot  keeps  on  contracting  for  thirty-six  hours  or  more, 
the  amount  of  serum  cannot  be  estimated  till  this  time  has 
elapsed.  There  is  nearly  as  much  serum  by  weight  as  there 
is  clot  in  coagulated  blood.  As  the  chemical  composition  of 
serum  is  merely  that  of  plasma  less  the  fibrinogen,  one  de- 
scription will  suffice  for  both. 

Properties  and  chemical  composition  of  blood-plasma  :  Blood- 
plasma  is  a  straw-colored,  slightly  viscid  fluid,  of  a  specific 
gravity  of  1030,  and  alkaline  (slight)  reaction.  Another 
property  of  plasma  is  that  of  dotting,  to  be  discussed  later. 

Chemically,  plasma  consists  of  a  large  percentage  of  water, 
holding  in  solution  a  number  of  inorganic  salts,  of  which 
sodium  chloride  and  sodium  carbonate  are  the  most  abundant. 

Besides  the  inorganic  compounds,  the  plasma  is  rich  in 
three  proteids — serum-albumin,  fibrinogen,  and  paraglobulin. 

Serum-albumin  is  one  of  the  so-called  groups  of  native  al- 
bumins, and  represents  the  proteid  portion  of  our  food-supply 
after  digestion  and  absorption  into  the  blood  have  taken  place. 

Fibrinogcn  and  paraglobulin  belong  to  the  group  of  globu- 
lins. Their  source  of  origin  is  unknown.  Their  purpose  in 
circulating  blood  is  also  doubtful ;  but  they  may  be  a  source 
of  nitrogenous  food.  At  any  rate,  they  play  an  important 
part  in  the  coagulation  of  blood,  as  will  be  seen. 

Carbohydrates  in  solution  and/afe  in  suspension  or  saponi- 
fication  are  also  present  in  the  plasma.  These,  too,  have  been 
absorbed  from  the  alimentary  tract. 

Other  organic  bodies,  such  as  urea,  lecithin,  and  cholesterin, 
representing  waste-products,  are  held  in  solution  by  the  plasma. 

Carbon  dioxide  is  found  in  solution  in  the  plasma,  repre- 
senting the  result  of  oxidation  in  the  tissues.  This  gas  is 
found  in  both  arterial  and  venous  blood,  but  in  greater 
amount  in  the  latter. 


42  THE  BLOOD. 

Small  amounts  of  oxygen  and  nit  rot/en  are  also  found  in 
solution  in  the  plasma.  There  is  also  probably  a  yellow  pig- 
ment, independent  of  the  haemoglobin,  which  has  not  yet  been 
exactly  determined,  though  it  is  probably  e/tofcsferm.  Similarly 
the  odoroua  matter  which  gives  the  characteristic  smell  to  the 
blood  of  different  animals  has  not  yet  been  discovered. 

Gases  of  the  blood :  In  the  blood  as  a  whole  are  found  car- 
bonic acid,  oxygen,  and  nitrogen  gases,  there  being  from  50  to 
60  volumes  of  these  gases  collectively  in  100  volumes  of 
blood.  There  are  relatively  more  oxygen  and  less  carbonic  acid 
gas  in  arterial  than  in  venous  blood  ;  but  in  both  kinds  of 
blood  the  carbonic  acid  exceeds  the  oxygen  in  amount.  In 
arterial  blood  there  is  about  20  per  cent,  of  oxygen,  40  per 
cent,  of  carbonic  acid,  and  1  to  2  per  cent,  of  nitrogen  ;  while 
in  venous  blood  the  oxygen  forms  from  8  to  12  per  cent.,  the 

FIG.  13.  FIG.  14. 


Bowl  of  recently  coagulated  blood,  show-       Bowl  of  coagulated  blood  after  t  welvo 
ing  the  whole 'mass  uniformly  solidified  hours,  showing  the  clot  contracted 

(Dalton).  and    floating    in  the    fluid  serum 

t  Dalton). 

carbonic  acid  about  45  per  cent.,  and  the  nitrogen  the  same 
percentage  as  in  the  arterial.  Part  of  both  the  oxygen  and 
the  carbonic  acid  is  in  solution,  and  the  rest  in  weak  chemi- 
cal combination.  Probably  all  the  nitrogen  is  in  solution. 

Coagulation  of  blood:  If  blood  be  drawn  into  a  shallow 
vessel  and  exposed  to  the  air,  it  will  become  semisolid  at  the 
surface  in  two  or  three  minutes.  This  jelly-like  condition 
will  extend  to  the  sides  of  the  vessel,  and  then  throughout 
the  entire  mass,  so  that  if  the  vessel  be  inverted  the  blood 
will  not  flow  at  the  end  of  ten  to  fifteen  minutes  (Fig.  13). 


COAGULATION  OF  BLOOD. 


43 


Then  drops  of  pale  fluid  (serum)  begin  to  appear  at  the  sur- 
face, and  these  unite  to  form  an  amount  of  fluid  sufficient 
in  an  hour  to  float  the  clot,  which  meanwhile  is  contracting 
from  the  sides  of  the  vessel.  The  serum  continues  to  exude 
and  the  clot  to  contract  for  twenty-four  to  thirty-six  hours. 
The  color  of  the  clot  remains  red,  while  the  serum  has  a  pale 
straw  color  (Fig.  14). 

Clotting  is  due  to  the  formation  of  a  substance  called  fibrin, 
which  appears  as  a  mesh  of  fine  fibrils  and  soon  entangles  the 
corpuscles.  This  mesh  of  fibrin  contracts  and  squeezes  out 
the  watery  elements  of  the  blood  to  form  serum,  and  holds 
the  solid  compounds,  as  shown  by  diagram  as  follows : 


Blood. 


Plasma. 


Corpuscles. 


Serum. 


Fibrin. 

I 


Clot. 


Clotted  blood. 


Conditions  affecting  coagulation :  It  has  been  found  that 
some  conditions  hasten  and  others  retard  the  time  of  coagu- 
lation. 

Retard. 

Greater  heat  or  extreme  cold  re- 
tard or  entirely  check. 

Contact  with  living  tissues,  espe- 
cially bloodvessels. 

Absence  of  air  retards.  After 
death  by  asphyxia  blood  remains 
fluid. 

Agitation  of  vessel  retards. 

More  than  twice  the  bulk  of  water. 


Hasten. 
Moderate  warmth,  100°-120°  F. 

Contact  with  foreign  matters. 
Access  of  air. 


Kest. 

Addition  of  moderate  amounts  of 
water. 


Addition  of  viscid  substances — 
i.  e.,  glycerin,  syrup. 

Addition  of  neutral  salts,  about  2 
per  cent,  solution. 

Digestive  ferments. 

Strong  acids  or  alkalies. 


44  THE  BLOOD. 

Coagulation  of  blood — explanation  :  There  are  many  theories 
to  explain  why  the  blood  clots,  but  no  one  theory  is  perfectly 
satisfactory.  The  best  we  can  do  is  to  state  such  facts  as  are 
proven.  As  has  been  already  stated,  in  the  plasma  of  the 
blood  there  exists  a  proteid,  called  fibrinogen  ;  there  is  also  in 
the  plasma  a  true,  unorganized,  organic  ferment,  called  filn-in- 
ferment.  When  the  blood  is  withdrawn  from  the  living 
bloodvessels  the  fibrin-ferment  acts  on  the  fibrinogen  and 
converts  it  into  fibrin,  the  fibrin-ferment,  like  all  true  fer- 
ments, remaining  unchanged.  If  the  process  were  as  simple 
as  described,  there  would  be  no  difficulty ;  but  the  change 
from  fibrinogen  to  fibrin  under  the  action  of  fibrin-ferment 
does  not  take  place  unless  a  third  substance  is  present.  The 
third  ingredient  is  paraglobulin,  already  mentioned  as  exist- 
ing in  the  blood-plasma.  What  part  the  paraglobulin  plays 
is  unknown.  It  is  merely  a  proteid,  and  not  a  ferment,  and 
yet  is  unchanged  by  the  act  of  clotting.  A  possible  expla- 
nation is  that  the  paraglobulin  unites  with  and  renders  inert 
some  substance  (unknown)  which  prevents  the  formation  of 
fibrin  in  the  living  condition.  After  clotting  has  occurred 
the  unchanged  fibrin-ferment  and  the  paraglobulin  are  found 
in  the  serum ;  the  fibrinogen,  now  converted  into  fibrin,  is 
the  clot.  The  fibrin-ferment  and  paraglobulin  are  capable  of 
still  further  activity  if  brought  into  contact  with  a  fresh 
supply  of  fibrinogen.  As  to  the  origin  of  these  three  factors 
of  coagulation  there  is  no  good  explanation.  It  has  been 
suggested  that  the  leukocytes  are  the  source  of  supply  of  one 
or  more  of  the  three  substances,  particularly  fibrin-ferment. 
Certainly  coagulation  is  more  active  in  the  presence  of  leuko- 
cytes. 

In  addition  to  the  three  factors  given,  the  very  important 
presence  of  calcium  salts  must  not  be  forgotten.  Although 
not  an  organic  agent,  in  the  process  of  coagulation  the  calcium 
salts  blend  with  the  fibrinogen,  which  under  the  influence  of 
the  fibrin-ferment  becomes  the  fibrin. 

Blood-coagulum — />'(////  coat:  If  we  examine  under  the 
microscope  the  blood-clot  which  has  formed  under  ordinary 
circumstances,  it  is  seen  that  the  red  corpuscles  arc  caught  by 
the  meshes  of  fibrin  and  are  uniformly  distributed  through- 


BL  0  OD-COA  G  UL  UM. 


45 


out  the  clot.  Many  of  the  leukocytes  have  made  good  their 
escape  into  the  serum.  If  we  take  a  quantity  of  blood  (Figs. 
15  and  16)  and  retard  the  time  of  coagulation  (horse's  blood 
coagulates  more  slowly  than  human  blood),  we  note  that  the 
upper  part  of  the  clot  is  much  lighter  in  color.  This  is  called 
the  "  buify  coat."  The  explanation  of  its  formation  is  very 
simple.  Owing  to  retardation  of  the  coagulation,  the  red  cor- 
puscles have  had  a  chance  to  settle  toward  the  bottom.  When 
seen  under  the  microscope  the  upper  layer,  or  buify  coat,  of 
the  clot  is  found  almost  free  from  red  corpuscles. 


FIG.  15. 


FIG.  16. 


Vertical  section  of  a  recent  coagulum, 
showing  the  greater  accumulation  of 
blood-globules  at  the  bottom  (Dalton). 


Bowl  of  coagulated  blood,  showing 
the  clot  buffed  and  cupped. 


Why  blood  does  not  clot  in  the  blood-vessels  :  As  long  as  the 
endothelial  lining  of  the  blood-vessels  is  intact  the  blood  does 
not  clot ;  but  if  the  endothelium  is  injured,  a  clot  is  formed  at 
the  site  of  the  injury.  Just  what  check  on  coagulation  the 
endothelium  plays  is  unknown,  but  it  is  none  the  less 
positive. 

If  a  vein  of  some  animal,  preferably  a  horse,  be  carefully 
ligated  in  two  places  some  inches  apart,  the  blood  within  it 
will  not  coagulate  for  a  long  time,  provided  the  endothelium 
is  uninjured.  This  is  not  due  to  occlusion  from  the  air  sim- 
ply. If  such  ligated  vein  with  its  contained  blood  be  re- 
moved from  the  body  and  carefully  opened,  the  blood  may  be 
poured  from  it  into  another  vein  similarly  prepared,  just  as 
we  pour  fluid  from  one  test-tube  to  another.  Though  the 
blood  is  thus  exposed  to  the  air,  it  will  not  coagulate  till  the 
endothelium  is  injured  or  loses  its  vitality. 


-10  THE  LYMPH. 

If  one  accepts  the  theory  that  the  fibrin-ferment  is  the  re- 
sult of  disintegration  of  leukocytes,  it  is  clear  why  Mood  does 
not  clot  within  the  bloodvc^els,  lor  then-  is  no  ferment  unless 
a  leukocyte  disintegrates,  the  "  normal  "  destruction  of  leuko- 
oytes  being  disregarded  as  a  possible  factor,  owing  to  the 
small  Dumber  so  destroyed  at  any  given  time.  On  the  other 
hand,  if  the  endothelium  be  wounded,  the  leukocytes  rush  to 
the  breach  and  are  broken  up;  also,  if  the  blood  is  shed, 
many  leukocytes  disintegrate  in  mass;  thus  in  both  instances 
a  large  amount  of  fibrin-ferment  is  liberated  and  clotting 
begins. 

Blood — resume  of  its  uses  :  The  red  corpuscles  convey  oxygen 
from  the  lungs  to  the  tissues. 

The  platnna  conveys  the  food,  after  absorption  from  the 
alimentary  canal,  to  the  tissues.  The  pla.-ma  also  holds  in 
solution  the  carbon  dioxide  and  water  (the  result  of  oxidation) 
which  it  receives  from  the  tissues,  and  carries  these  products 
to  be  eliminated  by  the  skin,  lungs,  and  kidneys.  The 
plasma  also  holds  in  solution  the  urea  and  other  nitrogenous 
bodies  that  are  carried  to  and  excreted  by  the  liver  and 
kidneys. 

The  leukocytes  are  protectors  against  the  invasion  of  bac- 
teria. 

Thus  it  is  seen  that  the  various  factors  of  the  blood  make 
up  a  whole — that  is,  a  conveyor  of  supplies,  a  remover  of 
waste,  and  a  protector  from  invasion. 

THE  LYMPH. 

Lymph  is  a  pale  straw-colored  fluid  that  bathes  all  the  tiny 
tissue-spaces  of  the  body  and  is  conveyed  by  lymph-vessels 

from  the  lymph-spaces  to  the  blood.      It  is  slightly  alkaline, 
<>f  a  salty  taste,  and  has  no  odor. 

Composition  :  Lymph  may  be  compared  to  a  dilute  blood 
free  from  r<-d  corpuscles,  but  rich  in  leukocytes.  "When  the 
lymph-vessels  of  the  lower  animals,  such  MS  tadpole-,  are  ex- 
amined under  the  microscope,  it  is  found  that  the  leukocytes 
are  only  present  in  the  larger  Trunks;  the  smallest  channels 
rarely  contain  particles  «>r  corpuscles  of  any  kind.  It  is  not 


THE  LYMPH.  47 

meant  that  all  the  constituents  of  blood  are  equally  reduced 
when  lymph  is  spoken  of  as  a  dilute  form  of  blood.  About 
the  same  proportions  of  salts,  urea,  and  sugar  are  present  in 
blood  and  lymph.  Only  about  one-half  as  much  serum- 
albumin  and  paraglobulin,  and  about  one-quarter  as  much 
fibrinogen,  are  in  lymph  as  are  present  in  blood.  Dnrin(/ 
digestion  there  is  a  marked  increase  in  fats  and  at  such  times 
the  appearance  of  the  lymph  from  the  intestines  is  like  milk, 
instead  of  being  straw-colored.  This  form  of  lymph,  known 
as  chyle,  owes  its  opacity  to  the  distribution  of  this  fatty 
matter  in  innumerable  particles  of  very  minute  though 
nearly  uniform  size,  measuring  about  -g-o-jyo^oth  °^  an  incn« 
Each  particle  is  coated  over  with  albumin. 

Lymph  coagulates  in  the  same  manner  as  blood,  but  more 
slowly  and  more  feebly ;  a  difference  readily  explained  by 
the  marked  difference  in  amount  of  fibrinogen  present.  This 
property  of  coagulation  is  not  possessed  by  the  lymph  in  the 
smallest  lymph-spaces  nor  by  the  chyle  in  the  villi  or  lacteals 
near  them.  It  is  only  developed  as  the  fluids  near  the  tho- 
racic duct. 

Lymph — sources:  Between  the  individual  capillaries  of  the 
blood-system  there  exist  small  intercellular  spaces,  into 
which  the  fluid  portions  of  the  blood  are  exuded  owing  to  the 
differences  in  pressure.  This  exudate,  plus  the  leukocytes 
that  have  left  the  bloodvessels  by  emigration,  makes  up  the 
lymph  proper.  In  addition  to  the  lymph  proper,  the  lymph 
that  fills  the  lacteals  of  the  intestinal  villi  absorbs  some  of 
the  products  of  digestion,  especially  the  fats.  This  portion 
of  the  lymph  that  has  absorbed  the  fats  is  milky  in  appear- 
ance, and  is  called  "  chyle.'7  The  chyle  and  lymph  proper 
are  carried  along  in  their  respective  channels  and  are  min- 
gled together  just  before  the  entire  fluid  is  poured  into  the 
vein  at  the  root  of  the  neck. 

Uses:  The  lymph  bathes  all  portions  of  the  body  not 
reached  by  the  blood.  Hence  the  lymph  conveys  the  nu- 
trient ingredients  of  the  blood  to  all  cells  not  directly  bathed 
by  the  blood.  The  "  chyle/'  or  lymph  of  digestion,  absorbs 
nutrient  materials  (mostly  fat)  from  the  intestines  and  pours 
this  food  into  the  blood-current,  to  be  universally  distributed. 


48 


CIRCULATION  OF  THK   JlLOOh. 


The  lymph  gathers  up  the  waste-materials  of  the  cells  sur- 
rounding the  lymph-spaces  and  pours  this  waste  into  the 
blood,  to  be  eliminated  by  the  skin,  lungs,  and  urine. 


CIRCULATION  OF  THE  BLOOD. 

The  circulation  of  the  blood  is  the  course  which  the  blood, 
as  a  transporting  medium,  follows  in  taking  food  and  air  to 
the  tissues  and  bringing  away  the  used-up  material  for  ex- 
cretion, and  returning  when  freshly  charged  with  oxygen  and 
food. 


FIG.  17. 


J.  V. 


Subcl. 
artery. 


Lungs. 


Lungs. 


Heart  and  lungs  of  man  (Milne  Edwards),  r.  a.,  right  auricle;  v.,  vena  mv.i  in- 
ferior; a.,  right  ventricle  ;  r.,  aorta  ;  I.  v.,  left  ventricle  ;  j.  v.,  jugular  vein  ;  c.  a., 
trachea  and  carotid  artery. 

The  circulatory  apparatus  consists  of: 

(1)  The  heart,  which  propels  the  blood  ; 

(2)  The  arteries,  which  convey  it  from   the   heart    to  the 
different  parts  of  the  body ; 


COURSE  OF  THE  BLOOD. 


49 


(3)  The   capillaries,  a 
network    of  inosculating 
tubules  interwoven  with 
the  substance  of  the  tis- 
sues   and    bringing    the 
blood  into  intimate  con- 
tact with  it ; 

(4)  The    veins,    which 
collect  the  blood  from  the 
capillaries  and   return  it 
to  the  heart. 

Course  of  the  blood  :  As 
the  motion  of  the  blood 
is  in  a  circle,  it  is  imma- 
terial at  what  part  of  the 
vascular  system  we  begin 
its  study.  Starting,  for 
convenience,  with  the 
blood  as  it  leaves'  the 
lungs,  we  find  that  the 
blood  enters  into  the  left 
auricle  from  the  pulmon- 
ary veins,  thence  passing 
the  open  mitral  valve  into 
the  left  ventricle  (Figs. 
17  and  18).  Upon  con- 
traction of  the  ventricle 
the  mitral  valve  is  closed 
and  the  aortic  valves 
thrown  open,  so  that  the 
blood  is  thrown  into  the 
aorta,  and  thence  through 
the  systemic  arterial  cir- 
culation into  capillaries 
and  on  into  veins,  the 
systemic  veins  finally 
joining  to  fill  the  venae 
cavre,  and  from  them  the 
right  auricle.  From  the 

4— Phys, 


50 


CIRCULATION  OF  THE  BLOOD. 


right  auricle  the  blood  passes  the  tricuspid  valve  into  the 
right  ventricle,  whence  it  is  thrown  through  the  pulmonary 
artery  (guarded  by  the  .pulmonary  semilunar  valves)  into  the 
pulmonary  capillaries,  and  thence  into  the  pulmonary  veins, 
whence  it  started.  Thus  we  have  in  reality  two  circulations, 
the  systemic  and  the  pulmonary. 

Also  we  see  that  the  blood  goes  through  one  set  of  capil- 
laries— the  lungs — to  be  purified  of  waste-products  and  re- 

FIG.  19. 


Anterior  view  of  heart  (Quain). 

oxygenated ;  and  another  set — the  systemic  capillaries — where 
the  oxygen  is  lost  and  the  waste-products  gathered  up. 

Furthermore,  the  student  will  take  note  that  the  blood 
which  enters  the  splenic  and  intestinal  arteries  from  the  aorta 
passes  through  fim  ,sv7x  of  capillaries  before  returning  to  the 
general  venous  circulation:  the  Jirxf  *<t  of  capillaries  is  in 
the  (t/iiiH-iiftirif  caiid/  and  .vyVro/,  whence  the  blood  return-,  is 
jin  the  portal  vein,  and  carried  to  the  liver.  In 


THE  HEART. 


51 


FIG.  20. 


the  latter  organ  the  blood  passes  through  a  second  set  of 
capillaries,  to  be  gathered  into  the  hepatic  veins,  and  finally 
emptied  into  the  inferior  vena  cava.  While  in  the  first  set 
(intestinal)  of  capillaries  the  blood  gives  up  its  oxygen  to 
nourish  the  walls  of  the  intestine,  and  takes  up  in  exchange 
the  carbon  dioxide  (waste  of  intestinal  activity)  and  certain 
of  the  nourishing  products  of  digestion.  On  passing  through 
the  hepatic  capillaries  some  of  the  food-products  are  left  be- 
hind in  the  liver  for  storage,  while  others  are  carried  on  into 
the  circulation. 

The  heart  (Fig.  19)  is  a  muscular  organ  situated  in  the 
thorax,  where  it  lies  between  the  lungs  within  the  pericardial 
sac,  and  rests  upon  the  diaphragm,  its  larger  portion  lying 
somewhat  to  the  left  of  the  midline  of  the  body.  It  is  coni- 
cal in  form,  and  is  so  suspended  by  the  great  vessels  that  the 
apex  points  to  the  left  and  downward.  Its  size  is  about 
that  of  the  closed  fist  (weight,  in  adults,  about  ten  ounces). 

It  is  divided  by  a  septum 
into  two  cavities,  not  con- 
nected, the  right  and  the  left 
(Fig.  20).  Each  of  these  in 
turn  is  subdivided  into  two 
parts,  the  auricle  and  the 
ventricle. 

The  auricles  are  thin- 
walled  cavities,  whose  func- 
tion is  to  receive  the  blood 
from  the  veins  and  pour  it 
into  the  ventricles. 

The  ventricles  are  sur- 
rounded by  the  most  power- 
ful portions  of  the  heart-muscle,  the  walls  of  the  left  being 
much  stronger  and  thicker  than  those  of  the  right  ventricle. 
The  auricles  contain  about  four  ounces,  the  ventricles  about 
six  ounces. 

Action  of  the  auricles :  During  the  period  of  rest  of  the 
heart,  blood  flows  freely  from  the  veins  into  the  auricles  and 
thence  into  the  ventricles,  the  auriculo-ventricular  valves 
offering  no  resistance ;  but  the  influx  is  so  strong  that  by  the 


Transverse  section  of  a  bullock's  heart 
in  the  state  of  cadaveric  rigidity,  a, 
cavity  of  the  left  ventricle ;  b,  cavi'ty  of 
the  right  ventricle. 


52 


CIRCULATION  OF  THE  BLOOD. 


time  the  heart  begins  to  contract  the  auricle  is  quite  filled  and 
the  ventricle  partially.  The  contraction  of  the  auricle  is  sud- 
den and  very  quick,  commencing  at  the  great  veins  aixl  ex- 
tending toward  the  ventricular  opening.  Both  auricle.-  con- 
tract simultaneously.  There  are  no  valves  at  the  openings  of 
the  venae  cavse  into  the  auricles,  but  the  blood  r/orx  not  r<(/nr</i- 
tate  for  the  following  reasons  : 


FIG.  22. 


Course  of  blood  through  the  heart.  Valves  of  the  heart, 

a,  a,  venn  cava,  superior  and  infe- 
rior ;  b,  ritfht  ventricle  ;  c,  pulmonary 
artery ;  <7,  pulmonary  vein ;  e,  left 
ventricle ;  /  aorta. 

(1)  The  power  of  the  auricular  contraction  is  not  sufficient 
to  cause  a  reflux. 

(2)  The  muscular  coat  of  the  great  veins  near  the  heart 
contracts,  and  helps  to  prevent  this  regurgitation. 

(3)  The  weight  of  the  incoming  blood  opposes. 

(4)  Valves  in  the  veins  oppose,  and  the   Eustachian  valve 
partially  guards  the  inferior  vena  cava. 

Action  of  the  ventricles:  The  ventricle  is  distended  during 
its  period  of  rest  by  the  flow  of  the  blond  from  the  veins  and 
by  the  auricular  contraction;  and  its  contraction  seems  con- 
tinuous with  that  of  the  auricle,  so  immediately  dors  it  sue- 


THE   VALVES.  53 

ceed.  The  ventricular  contraction  is  slower  and  probably 
completely  empties  the  cavity.  The  ventricles  contract  si- 
multaneously. The  shape  of  the  ventricles  is  changed  :  as  the 
heart-muscle  becomes  hard  and  rigid  in  contraction  the  section 
of  its  base  becomes  circular,  instead  of  elliptical,  as  it  is  dur- 
ing repose ;  the  ventricles  shorten  and  twist  to  the  right,  and 
the  form  is  conical.  As  the  organ  relaxes  it  returns  to  its 
former  position  and  shape,  that  of  a  cone  with  elliptical  base. 
This  shortening  of  the  ventricles  in  contraction  is  compen- 
sated by  the  lengthening  of  the  great  vessels  at  the  base  as 
they  become  distended  by  the  load  of  blood. 

The  valves :  In  considering  the  functions  of  the  valves  of 
the  heart  one  must  bear  in  mind  constantly  that  the  organ  is 
a  pump  whose  office  is  to  force  the  blood  in  one  direction. 
There  are  four  principal  valves — two  auriculo- ventricular, 
and  two  in  the  great  arteries,  the  aorta  and  the  pulmonary 
artery  :  (1)  As  the  ventricle  fills  the  auriculo-ventricular  valves 
are  floated  up  from  the  sides  of  the  ventricle  in  such  manner 
that  their  edges  are  in  contact,  cusp  to  cusp.  As  the  ventricle 
contracts  more  violently,  pressure  is  brought  upon  the  valve, 
so  that  not  only  is  the  edge  in  contact,  but  also  portions  of 
the  surfaces  of  the  cusps.  These  valves  are  of  considerable 
area,  and  are  guyed  in  position  by  the  chordce  tendinece,  which 
spring  from  the  papillary  muscles,  so  that  e version  of  the 
valve  into  the  auricle  is  impossible.  (2)  The  semilunar  valves 
form  a  guard  against  the  return  of  the  blood  to  the  ventricle 
at  the  pulmonary  and  aortic  openings  of  the  ventricles.  These 
valves  are  forced  open  by  the  ventricular  contraction,  and 
through  them  the  blood  rushes  to  distend  the  elastic  walls  of 
the  large  arteries.  The  pressure  of  the  blood  under  this 
elastic  grasp  is  sufficient  to  throw  the  cusps  of  the  valves  into 
action.  The  corpora  Arantii  are  useful  in  making  a  perfect 
closure  of  the  valve,  though  not  absolutely  essential.  A  part 
of  the  weight  of  this  pressure  is  borne  by  the  thick  ventricu- 
lar wall,  which  forms  a  ring,  from  the  outer  edge  of  which 
the  artery  springs,  while  the  valves  are  attached  to  the  inner 
edge. 

Under  some  circumstances  the  tricuspid  valve  does  not  en- 
tirely close,  but  allows  a  certain  amount  of  regurgitation  of 


54  CIRCULATION  OF  THE  BLOOD. 

blood.  This  occurs  in  conditions  of  disease  or  of  violent  ex- 
ertion, in  which  the  lung-capillaries  are  overcharged  with 
blond.  The  leakage  of  the  valve  is  conservative,  and  relieves 
the  prcs-urc  upon  the  delicate  capillaries  of  the  pulmonary 
alveolae.  Pulsation  in  the  jugular  veins  indicates  this  re- 
gurgitation.  The  condition  is  not  pathological,  and  with 
altered  conditions  disappears. 

The  arteries  are  continuous  hollow  tubes  leading  from  the 
heart.  They  are  surrounded  by  a  dense  fibrous  coat  exter- 
nally, and  are  lined  internally  by  a  smooth  endothelial  lining; 
between  these  is  an  elastic  layer  of  fibrous  tissue,  which  has 
interlaced  in  its  structure  muscle-cells  arranged  transversely 
around  the  vessel.  Each  artery  has  its  own  vasa  vasorum, 
or  nutrient  vessels,  and  is  usually  enmeshed  in  a  plexus  of 
sympathetic  nerves,  "vaso-motor"  nerves.  Owing  to  the 
various  branches  given  off  from  the  arteries,  the  calibre 
of  these  vessels  diminishes  as  we  leave  the  heart.  The 
smallest  arteries  have  been  designated  artei'ioles,  and  at 
their  distal  ends  the  arterioles  cease  and  the  capillaries 
begin. 

In  the  large  arteries  the  elastic  tissue  is  in  excess  of  the 
muscle-tissue,  whereas  the  reverse  holds  true  in  the  arterioles. 
The  principal  difference  between  the  larger  and  the  sm a  1  lei- 
arteries  is  in  the  structure  of  their  middle  coat.  In  the 
smaller  arteries  this  is  composed  exclusively  of  muscular 
fibres.  In  arteries  of  medium  size  it  contains  both  muscular 
and  elastic  tissue ;  while  in  those  of  the  largest  calibre  it 
consists  of  elastic  tissue  alone.  The  larger  arteries,  accord- 
ingly, have  much  elasticity  and  but  little  contractility  ;  while 
the  smaller  are  contractile  and  less  elastic.  The  variation  in 
thickness  of  this  middle  coat  is  chiefly  responsible  for  t In- 
differences in  the  thickness  of  the  walls  of  the  larger  and 
smaller  arteries. 

The  capillaries  :  The  capillary  blood-vessels  (Fig.  23)  are 
channels  of  very  small  but  variable  size,  but  usually  of  about 
sufficient  calibre  to  permit  just  the  passage  of  the  red  and 
white  corpuscles.  They  are  usually  composed  of  a  single 
layer  of  endothelial  cells  joined  at  the  edges,  though  near  the 
arteries  and  veins  there  is  sometimes  an  elastic  fibrous  coat. 


SIZE  OF  THE  BLOODVESSELS. 


55 


A  sympathetic  nerve-plexus  surrounds  these  vessels.  The 
capillaries  form  a  complicated  network  in  the  tissues,  and  the 
mesh  of  the  net  varies  in  shape  and  size  greatly  with  the  vas- 
cularity  and  function  of  the  tissue. 

The  veins  :  In  structure  the  veins  are  similar  to  the  arteries, 
being  composed  of  three  coats — an  inner,  a  middle,  and  an 
exterior — of  similar  nature  ;  but  they  contain  a  smaller  quan- 
tity of  muscular  and  elastic  fibres  and  a  larger  portion  of 
condensed  connective  tissue. 
That  is,  their  inner  and  middle  FIG.  24. 


FIG.  23. 


Fine  capillaries  from  the  mesen- 
tery. 


Diagram  showing  valves  of  veins.  A, 
part  of  a  vein  laid  open  and  spread 
out,  with  two  pairs  of  valves.  B, 
longitudinal  section  of  a  vein, 
showing  the  apposition  of  the  edges 
of  the  valves  in  their  closed  state. 
C,  portion  of  a  distended  vein,  ex- 
hibiting a  swelling  in  the  situation 
of  a  pair  of  valves  (Quain). 


coats  are  thin,  while  the  outer  coat  is  relatively  thick.  Con- 
sequently they  are  less  elastic  and  contractile,  but  more  com- 
pressible than  arteries.  Veins  collapse,  while  arteries  remain 
open  when  not  distended  by  blood.  Valves  (Fig.  24)  occur 
in  most  of  the  veins  ;  these  are  so  placed  as  to  prevent  the 
blood  from  tending  to  flow  backward.  The  valves  are  so 
placed  as  to  aid  the  onward  progress  of  the  blood  in  the  veins, 
the  pressure  of  neighboring  muscles  forcing  forward  the  blood, 
which  cannot  regurgitate  past  the  valves. 

Size  of  the  bloodvessels  :  With  the  division  of  the  arteries 


56  CIRCULATION  OF  THE  BLOOD. 

into  branches  the  sectional  area  of  the  branches  is  greater  than 
that  of  the  stem.  Of  the  veins  the  same  is  true,  while  the 
total  sectional  area  of  the  capillary  system  is  much  greater 
than  that  of  either.  For  purposes  of  simile  the  comparison 
may  be  made  of  two  funnels  placed  base  to  base.  In  numbers 
one  may  consider  the  sectional  area  of  the  aorta  as  1  ;  of  the 
venae  cavae,  2  or  3  ;  of  the  capillaries,  (about)  500.  An  in- 
dividual capillary  has  been  estimated  as  being  i  mm.  long, 
and  from  5  to  20 /n  in  diameter. 

Forces  maintaining  circulation:  The  heart,  as  has  been 
shown,  is  a  force-pump,  and  at  each  contraction  injects  a 
fresh  volume  of  blood  into  the  arteries  ;  during  the  repo^-  <>f' 
the  heart  it  fills  up  with  blood  from  the  veins  which  has 
already  travelled  the  circuit. 

The  heart  is  the  prime  and  important  factor  in  maintaining 
circulation,  and  is  capable  of  forcing,  unaided,  the  blood 
through  the  entire  circuit  ;  but  in  addition  we  find  suh^'ulitirii 
forces  assisting  the  outward  flow  of  blood  : 

(1)  Arterial  resiliency :  At  each  beat  the  ventricles  inject  a 
fresh  quantity  of  blood  into  the  already  filled  arteries.     To 
make   room   for  this   surcharge  of  blood  the   large   arteries, 
owing  to  their  elasticity,  are  dilated  by  the  increased  amount 
of  blood.     During  the  repose  of  the  heart  the  arteries  con- 
tract by  virtue  of  the  recoil  of  their  elastic  fibres  and  drive 
the  blood  on.     This  action  of  the  arteries  converts  the  inter- 
mittent character  of  the  blood-stream  into  a  steady  flow  by 
the  time  the  capillaries  are  reached. 

(2)  Contraction  of  muscles:  The  skeletal  muscles,  during 
the  ordinary  activities  of  the  body,  contract,  and  so  compress 
the  veins  lying  between  them.     This  compression  drives  the 
blood  out  of  the  veins,  but  only  in  the  proper  direction,   as 
the  valves  of  the  veins  prevent  the  reverse  flow. 

(3)  Cardiac  suction :  During  the  period  of  repose  the  open- 
ing out  of  the  heart-cavity   is  sufficiently  strong  to  exert  a 
decided  suction  on  the  blood  in  the  veins. 

(4)  Thoracic  suction:  During   the  expansion  of  the  chest 
in  inspiration  a  tendency  to  a  vacuum  is  produced,  which  ex- 
erts a  suction  on  the  large  veins  within  the  thoracic  cavity. 
This  fact   must  always  be  borne  in  mind   by  the   surgeon 


BLOOD-PRESSURE.  57 

when  operating  on  the  neck.  Should  a  large  vein  be  wounded, 
it  must  be  instantly  closed,  lest  by  reason  of  this  suction 
air  be  drawn  into  the  vein.  If  air  should  in  this  way 
enter  the  proximal  part  of  a  wounded  vein,  it  would  be  hur- 
ried along  to  the  heart,  and,  there  expanding,  cause  serious 
trouble  or  even  death. 

(5)  A  slight  rhythmical  contraction  of  the  veins. 

Speed  of  the  blood :  In  the  arteries  it  has  been  estimated 
that  the  blood  in  the  large  arteries  travels  at  the  rate  of  about 
300  to  500  mm.  per  second.  As  the  blood  advances  in  the 
arteries  the  speed  decreases  gradually. 

In  the  capillaries,  owing  to  their  much  larger  aggregate 
diameter  (500 :  1),  the  speed  falls  very  low,  and  is  estimated 
to  be  f  of  a  mm.  per  second. 

In  the  veins  the  speed  increases  as  we  approach  the  heart, 
and  in  the  venae  cavse  is  found  to  be  from  125  to  200  mm. 
per  second. 

With  these  figures  as  a  basis,  it  has  been  calculated  that  a 
given  particle  of  blood  occupies  about  a  half  minute  of  time 
in  going  the  round  of  the  body.  One  second  of  the  half  min- 
ute is  used  in  passing  the  systemic  capillaries,  another  second 
in  traversing  the  pulmonary  capillaries. 

It  has  been  found  by  experiment  on  animals  that  there  is 
a  ratio  between  the  blood-speed  and  -pressure  which  may  be 
direct  or  inverse.  Any  influence  which  increases  or  dimin- 
ishes the  force  of  the  heart  will  at  the  same  time  increase  or 
diminish  both  the  velocity  and  the  pressure  of  the  blood  ; 
while  any  influence  which  increases  or  diminishes  the  re- 
sistance to  the  arterial  flow  will  make  the  velocity  and  the 
blood-pressure  vary  in  an  inverse  ratio  to  each  other.  Other 
things  being  equal,  both  the  pressure  and  the  velocity  in  the 
large  arteries  increase  markedly  during  systole  and  diminish 
greatly  during  diastole.  Very  near  the  heart  the  velocity  is 
greatest  at  the  beginning  of  systole,  then  drops  to  almost 
nothing  toward  the  end  of  systole,  and  then,  regaining  speed, 
flows  at  an  almost  even  pace  during  diastole  (Fig.  25). 

Blood-pressure  :  By  means  of  manometers  the  blood-pressure 
has  been  determined.  It  is  greatest  in  the  arteries  nearest 
the  heart,  and  gradually  diminishes,  until  in  the  veins  empty- 


58 


CIRCULATION  OF  THE  BLOOD. 


ing  into   the  heart  it  is  found  to  be  zero ;  or  even  a   slight 
negative  pressure  or  suction  may  be  present. 

The  figures  are  as  follows :  pressure  in  the  large  arteries 
supports  a  column  of  mercury  150—200  mm.  Iiiirh  (about  four 
pounds  to  the  square  inch).  In  the  capillaries,  30—50  mm. 
of  mercury.  In  the  distal  veins,  20  mm.  of  mercury,  gradu- 
ally falling  as  we  approach  the  heart. 


1     234 


1    23  4 


1    234 


Tracings  of  variations  of  rapidity  and  of  pressure  of  blood  in  the  carotid  of  a  horse, 
obtained  by  Chauveau  and  Lortet.  The  line  v  represents  tin-  curve  of  the  ra- 
pidity of  the  blood  ;  and  p  the  curve  of  arterial  pressure.  The  h'gun  <  aixl  vi -r- 
tical  lines  represent  corresponding  periods  in  the  tracings  (McKnidrirk  i. 


The  cause  of  the  high  pressure  in  the  arteries  is  due  to  the 
force  of  the  blood  injected  from  the  heart  behind,  and  the  re- 
sistance of  the  capillaries  in  front.  Although  the  blood  is 
pumped  into  the  arteries  in  intermittent  jets,  when  a  *//>"// 
artery  is  cut  the  blood  spurts  from  it  in  a  continuous  jet.  The 
reason  for  this  is  the  elasticity  of  the  arterial  walls,  these1 
being  put  on  the  stretch  by  the  blood  forced  into  them  at  con- 
siderable pressure,  and  contracting  again  during  the  period  of 
heart-rest,  thus  enabling  the  arteries  to  keep  the  blood  under 
elastic  compression.  The  capillaries,  though  collectively  of 
much  greater  area  than  the  arteries,  by  reason  of  the  friction 
they  offer  to  the  blood-stream  maintain  a  less  degree  of  ten- 
sion. 


THE  BLOOD  IN  CIRCULATION.  59 

Conditions  modifying  arterial  tension :  (1)  The  rate  of  the 
heart-beats,  by  keeping  the  arteries  fuller  or  less  full,  will 
modify  the  blood-pressure  in  the  arteries. 

(2)  Vaso-motor  changes,  by  increasing  or  decreasing  the 
friction  offered   the  arterial   blood,  vary  the  tension  in  the 
arteries. 

(3)  The  amount  of  blood  in  the  system  must  to  a  great 
extent  determine   the  limits  of  arterial  pressure.     In  great 
exsanguination  the  arterial  pressure  is  quite  low. 

(4)  Motion  of  the  thoracic  walls  in  breathing  necessarily 
changes  the  arterial  tension  by  the  pumping  force  exerted  by 
this  motion. 

The  blood  in  circulation :  While  circulating  in  the  arteries 
and  veins  the  blood  travels  at  too  great  a  speed  to  admit  of 
careful  examination  ;  the  leukocytes  in  spherical  form  and 
the  red  corpuscles,  bowled  along  indiscriminately,  pass  the  eye 
too  rapidly  for  any  peculiarities  to  be  noticed. 

The  capillaries  of  the  web  of  a  frog's  foot  can  be  easily 
examined  with  a  microscope.  In  these  the  speed  of  the  blood 
is  slow,  and  ample  time  is  given  to  study  the  particular  cor- 
puscles. 

On  entering  the  capillaries  the  red  cells  are  seen  to  occupy 
the  central  portion  of  the  stream  of  plasma.  That  portion 
of  the  plasma  in  contact  with  the  capillary  walls  is  seen  to 
travel  much  slower  than  the  central  portion,  owing  to  the 
friction  presented  by  the  capillaries.  This  is  known  as  the 
"  inert  layer "  of  plasma.  The  corpuscles,  being  compara- 
tively heavy,  are  crowded  in  the  centre  of  the  stream.  That 
the  centre  of  the  stream  travels  faster  than  the  periphery  is 
shown  by  the  fact  that  if  we  watch  three  corpuscles  floating 
abreast,  in  a  moment  or  two  the  centre  corpuscle  forges  ahead 
and  leaves  its  companions  behind. 

Some  of  the  capillaries  are  so  small  that  the  red  corpuscles 
pass  in  single  file ;  some  may  even  be  so  small  that  the  cor- 
puscle is  squeezed  up  and  elongated  that  it  may  glide  through 
the  constriction ;  on  entering  a  vessel  of  larger  calibre  the 
corpuscle,  owing  to  its  elasticity,  resumes  its  shape. 

The  leukocytes  in  the  arteries  are  carried  along  passively  in 
spherical  shape,  but  on  entering  the  capillaries  are  crowded 


60 


CIRCULATION  OF  THE  BLOOD. 


into  the  inert  layer  by  the  heavier  red  corpuscles.  In  the 
inert  layer  they  change  their  shape  and  flatten  out  against 
the  capillary-wall.  They  now  exhibit  their  am<eboid  move- 
ment, and  perchance  one  may  be  seen  sending  its  pseudo- 
podia  through  the  cement-substance  between  the  endothelial 
cells  of  the  capillary-wall — in  other  words,  puncturing  the 
capillary.  Having  projected  a  pseudopod  through  the  capil- 

FIG.  26. 


Capillary  plexus  in  a  portion  of  the  web  of  a  frog's  foot  (magnified  110  diameters). 
1,  trunk  of  vein;  2,  2, 2,  its  branches ;  3,  3,  pigment-cells. 

lary-wall,  the  leukocyte  proceeds  to  draw  the  rest  of  its  body 
through,  and  then  escapes  into  the  tissue-spaces.  The  cement- 
si  ibstance  closes  spontaneously  and  no  leak  occurs. 

Of  course,  it  must  not  be  supposed  that  all  the  leukocytes 
escape  from  the  capillaries.  Only  a  small  portion  undergo 
this  "  emigration,"  the  majority  going  on  with  the  blood- 
current  into  the  veins  (Fig.  26). 


ACTION  OF  HEART. 


61 


The  Heart  (see  also  p.  51). 

Action  of  heart:  During  ordinary  average  life  the  heart 
beats  about  72  times  per  minute.  During  muscular  activity 
and  after  eating  or  under  excitement  the  rate  increases ; 


FIG.  27. 


FIG.  28. 


Projection  of  a  dog's  heart.  Shaded  portion  indicates  appearance  of  diastole; 
white  portion,  of  systole.  A,  anterior  surface;  L,  lateral  surface;  P,  poste- 
rior surface  (McKendrick). 

during  sleep  it  is  lowered.     At  birth  it  is  about  130  per  min- 
ute ;  at  three  years,  100 ;  in  adult  life,  72 ;  in  old  age,  65. 

This  rate  is  varied  from  time  to  time 
by  conditions  of  bodily  health  and  by 
environment.  The  heart-beat  in  women 
is  somewhat  more  rapid  than  in  men. 
The  relative  frequency  of  heart  and 
respiratory  action  is  about  three  or  four 
heart-beats  to  one  respiratory  act. 

The  heart-beat^  is  made  up  of  a  con- 
traction— systole — and  a  repose — dias- 
tole. During  systole  the  heart  becomes 

hard  and  diminishes  in  size  not  only  Converging  spiral  fibres  at 
transversely,  but  longitudinally  (Fig. 
27),  thus  resembling  voluntary  muscle. 
This  can  be  proved  by  experiment, 
though  it  seems  false  to  any  one  who 
has  examined  a  heart  while  in  place  in  a  living  animal.  In 
such  cases  there  is  an  apparent  elongation  of  the  heart  during 
systole,  due,  however,  to  the  forward  motion  of  the  whole 
heart  during  systole.  This  forward  motion  is  a  result  of 


the  apex  of  the  heart.  The 
direction  of  the  arrows  in- 
dicates that  of  the  rotat- 
ing movement  of  the  heart 
at  the  ventricular  systole. 


62  CIRCULATION  OF  THE  BLOOD. 

the  twisting  of  the  apex  of  the  heart  upon  itself  during  sys- 
tole (Fig.  28)  from  left  to  right,  returning  during  diastole. 
It  i-  caused  by  the  spiral  arrangement  of  the  muscular  fibres 
at  the  apex. 

The  combined  systole  and  diastole  is  called  the  <-ftr<//<ic 
<•//<•/,,  and  consists  of  four  factors  :  (1)  systole  of  the  auricles, 
(2)  diastole  of  the  auricles,  (3)  systole  of  the  ventricles,  and 
(4)  diastole  of  the  ventricles. 

The  auricular  systole  is  rapid,  and  forces  the  blood  into 
the  still  quiescent  ventricles.  On  completion  of  the  au- 
ricular systole  the  auricles  expand  and  remain  quiet  during 
the  systole  of  the  ventricles,  which  begins  the  moment  the 
auricles  cease  contracting. 

The  ventricular  systole  is  more  forcible  than  that  of  the 
auricles,  but  the  ventricles  remain  in  contraction  longer  than 
do  the  auricles.  During  ventricular  systole  the  blood  is 
forced  into  the  arteries.  At  the  close  of  the  ventricular 
systole  the  ventricles  dilate.  The  auricles  do  not  take  up 
work  again  at  once,  but  there  is  a  period  during  which  the 
entire  heart  is  in  repose.  After  this  repose  the  auricles  again 
contract  and  a  new  cycle  is  begun. 

Time  of  cycle  :  If  we  assume  the  average  heart-beats  to  be 
72  per  minute,  each  cardiac  cycle  occupies  0.8  of  a  second. 
The  contraction  of  the  auricles  lasts  0.1  of  a  second.  The 
contraction  of  the  ventricles  lasts  0.3  of  a  second  ;  and  the 
repose  of  the  entire  heart,  0.4  of  a  second.  Thus  of  the  en- 
tire 0.8  of  a  second,  the  auricular  systole  lasts  0.1  of  a  second 
and  the  diastole  0.7  of  a  second  ;  the  ventricular  systole  0.-'5  of 
a  second  and  the  diastole  of  the  ventricles  0.5  of  a  second. 
The  combined  systole  of  the  auricles  and  ventricles,  0.4  of  a 
second  ;  and  the  total  repose  of  the  whole  heart,  0.4  of  a 
second.  If  the  heart-rate  be  increased,  the  ventricular 
systole  remains  about  0.3  of  a  second :  so  we  see  that  an  in- 
crease in  the  heart-rate  is  made  at  the  expense  of  the  dias- 
tole. 

Heart-iounds :  The  first  sound  is  heard  best  over  the  apex 
of  the  heart.  It  is  of  a  dull,  prolonged,  booming  character. 
The  second  sound  is  heard  immediately  after  the  first,  and  is 
a  sharp,  quick,  almost  clicking  sound  ;  it  is  heard  most  clearly 


FORCE  OF  THE  HEART.  63 

over  the  base.  The  sounds  are  said  somewhat  to  resemble 
that  expressed  by  lubb-dup. 

The  first  sound  is  synchronous  with  the  ventricular  sys- 
tole and  with  the  closure  of  the  auriculo-ventricular  valves  ; 
it  is  supposed  to  be  made  up  in  reality  of  two  sounds — a  val- 
vular one,  caused  by  closure  of  the  auriculo-ventricular 
valves,  and  a  muffled  one,  due  to  contraction  of  the  muscular 
fibres  of  the  ventricles.  That  it  is  due  in  part  to  the  action 
of  the  valves  is  proved  by  the  fact  that  the  sound  is  altered 
when  the  valves  are  diseased  or  are  artificially  prevented 
from  closing.  That  muscular  contraction  of  the  heart  pro- 
duces a  sound  can  be  demonstrated  by  the  cardiophone.  This 
is  the  only  way  of  accounting  for  the  sound,  though  of  an 
altered  character  it  is  true,  which  is  produced  at  the  begin- 
ning of  systole  by  a  heart  from  which  the  auriculo-ventricu- 
lar valves  have  been  experimentally  removed. 

The  second  sound  is  synchronous  with  the  closure  of  the 
semilunar  valves,  and  is  caused  by  this  action.  It  is  heard 
most  distinctly  opposite  these  valves,  and  is  propagated  upward 
along  the  great  vessels  to  which  they  are  attached.  There  is 
no  doubt  that  it  is  caused  solely  by  their  closure. 

Blood-supply  of  the  heart :  By  the  coronary  arteries,  which 
arise  in  the  sinuses  of  Valsalva  circumferential  to  the  leaves 
of  the  semilunar  valves.  They  do  not  receive  blood  during 
systole ;  but  during  diastole  from  pressure  of  the  blood  due 
to  the  elasticity  of  the  arteries,  especially  that  of  the  aorta. 
The  blood  is  returned  to  the  right  auricle  through  the  coro- 
nary sinus  and  cardiac  veins. 

Force  of  the  heart :  The  left  ventricle  exerts  more  than 
twice  as  much  power  as  the  right.  The  exact  intra ventricu- 
lar pressure  in  man  has  not  been  ascertained.  The  expansion 
of  the  heart  exerts  a  negative  (or  suction)  pressure  which  aids 
the  onflow  of  the  blood,  especially  from  the  lungs  to  the  left 
auricle  and  ventricle.  The  intra-auricular  pressure  is  very 
much  less  than  the  intraventricular,  and  there  is  a  negative 
pressure  during  diastole  in  the  auricles. 

Estimated  in  foot-pounds,  each  ventricular  contraction  rep- 
resents three  and  a  half  to  four  and  a  half  foot-pounds.  In 
twenty-four  hours  this  is  estimated  to  equal  more  than  one 


64 


CIRCULATION  OF  THE  BLOOD. 


hundred  and  twenty  foot-tons.    In  another  light,  if  the  blood 
is  one-twelfth  of  the  body-weight,  and  if  the  amount  of  blood 


FIG.  29. 


Diagrammatic  view  of  the  nerves  influencing  the  action  of  the  heart.  The  right 
half  repri'.si-iits  the  course  of  the  inhibitory,  and  the  left  the  course  of  the 
accelerating  nerves  of  the  heart;  the  arrows  >h<;win^  tin-  direction  in  \\hiHi 
impressions  are  conveyed.  The  ellipse  :it  tin-  upper  extremity  of  the  vat-us, 
looking  like  a  section  of  the  nerre,  u  intended  to  represent  the  va^al  nucleus 
or  centre.  In  this  diagram  the  nerves  are  incorrectly  made  to  cross,  instead  of 
passing  behind,  the  m.rta. 

pumj^ed  with  each  ventricular  contraction  is  six  ounces,  in 
an  ordinary  man  an  amount  of  blood  equal  to  the  total  blood 


INNERVATION  OF  THE  HEART.  65 

of  the  body  will  pass  through  the  heart  in  about  half  a 
minute. 

The  amount  of  blood  poured  out  by  the  systole  of  the  ven- 
tricles is  called  the  "  pulse-volume." 

Innervation  of  the  heart  :  This  matter  is  somewhat  unde- 
cided at  present,  for  the  reason  that  many  of  the  results  must 
be  obtained  from  experiments  upon  the  hearts  of  cold- 
blooded animals.  We  do  know  that  the  mechanism  of  rhyth- 
mical contraction  is  contained  within  the  heart  itself.  Nerve- 
ganglia  are  demonstrated  in  the  frog's  heart  which  are  essen- 
tial to  its  action  ;  similar  ganglia  exist  in  the  human  heart. 
These  ganglia  are  connected  with  fibres  from  the  pneumo- 
gastric  (or  vagus)  nerve  and  with  the  sympathetic  system 
(Fig.  29). 

The  eardiac  inhibitory  nerve  is  a  branch  from  the  pneumo- 
gastric  nerve  running  to  the  heart.  It  has  an  inhibitory  or 
slowing  effect  upon  the  heart  ;  for  if  we  cut  the  nerve  the 
heart  becomes  more  rapid,  and  if  we  stimulate  (Fig.  30)  the 

FIG.  30. 


Effect  of  stimulation  of  the  pneumogastric  nerve  upon  the  action  of  the 
heart  in  a  frog.    To  be  read  from  right  to  left. 

peripheral  end  of  the  nerve  we  slow  the  heart  again.  This 
action  may  be  traced  to  the  medulla  oblongata,  where  a  cardio- 
inhibitory  centre  is  located.  That  the  inhibitory  influence  of 
the  cardiac  fibres  of  the  vagus  is  not  directly  exerted  upon 
the  heart  is  proven  by  the  length  of  time  elapsing  between 
the  application  of  the  stimulus  and  the  appearance  of  the  in- 
hibitory effect.  In  some  cases  even  two  entire  heart-beats 
occur  after  a  strong  stimulus  is  applied  before  the  heart  stops, 
indicating  that  some  resistance  must  be  overcome,  the  inhib- 
itory fibres  acting  upon  inhibitory  centres  in  the  heart  itself. 
Stimulation  of  the  vagus  not  only  slows  the  heart's  action, 
but  modifies  it.  Systole  and  diastole  are  lengthened  ;  the 
input  and  output  of  the  ventricle  are  diminished  ;  the  dias- 
tole pressure  and  volume  of  blood  in  the  ventricles  are  in- 

5—  Phys. 


66 


CIRCULATION  OF  THE  BLOOD. 


i 

1* 

8  a 

II 


creased,  and  ventricular  become  less  frequent  than  auricular 
(•(niti-actions,  the  latter  being  often  twice  as  numerous. 

(  'crtaiu  fibres  of  the  sympathetic  from  the  cervical  and  up- 
per dorsal  spinal  cord  pass  to  the  heart. 
If  these  fibres  are  left  after  all  other 
nerve-connections  of  the  heart  are  cut 
away,  stimulation  of  the  spinal  cord  will 
cause  the  heart  to  become  rapid.  These 
are  known  as  accelerator  nerves.  These 
accelerating  nerves  act  less  powerfully 
than  the  inhibitory  ones.  They  not  only 
accelerate  the  heart's  action,  but  in- 
crease the  force  of  the  beat  and  the  out- 
put (Fig.  31). 

The  cardiac  depressor  nerve  is  a  cen- 
tripetal nerve  running  from  the  heart  to 
the  vaso-motor  centre  in  the  medulla. 
Its  purpose  is  to  stimulate  the  vas«»- 
motor  centre  to  dilate  the  peripheral 
arteries.  The  nerve  is  "stimulating" 
only  when  the  heart  is  laboring  against 
too  high  tension  produced  by  unusually 
high  peripheral  resistance. 

Vaso-motor  Nerves. 

Arterial  contraction  and  dilatation : 
The  muscular  coats  of  the  peripheral 
arteries  do  not  undergo  a  rhythmical 
contraction  and  dilatation,  but  only  con- 
tract so  as  to  diminish  the  calibre  of  the 
arteries  and  thus  limit  the  supply  of 
blood  to  a  given  part  of  the  body.  On 
the  other  hand,  the  muscle-fibres  relax 
and  allow  the  arteries  to  dilate  when 
the  given  part  demands  more  blood  to 
satisfy  its  activities.  Hence  it  is  a  per- 
fectly normal  condition  to  have  the  arteries  of  one  part  of 
the  body  dilated,  while  the  arteries  supplying  another  part 


ACTION  OF  VASO-MOTOR  NERVES.  67 

are  contracted,  depending  on  which  part  of  the  body  is  func- 
tionating. 

By  tone  of  the  arteries  is  meant  their  average  normal  state 
of  contraction. 

The  nerve-supply  of  the  muscular  coats  of  the  arteries  is 
through  the  "  vaso-motor  "  nerves.  They  are  of  two  varie- 
ties according  to  their  function,  vaso-constrictor  and  vaso- 
dilator. These  nerves  (vaso-constrictor  and  vaso-dilator)  run 
together  in  the  same  sheath,  and  are  part  of  the  sympathetic 
system. 

They  have  their  origin  in  the  vaso-motor  centre  in  the 
medulla.  They  pass  down  the  spinal  cord  to  emerge  at  dif- 
ferent levels,  thence  to  be  distributed  to  all  the  different  ar- 
teries. Just  before  leaving  the  spinal  cord  there  are  second- 
ary vaso-motor  centres  in  the  course  of  these  nerves.  Close 
to  the  wall  of  the  artery  to  be  supplied  there  is  a  third  (gan- 
glionic)  centre  for  vaso-motor  action.  On  emerging  from  this 
third  centre  the  vaso-motor  nerve  breaks  up  into  its  terminal 
filaments  which  are  distributed  to  each  muscle-fibre. 

Action  of  vaso-motor  nerves :  It  must  not  be  supposed  that 
contraction  and  dilatation  of  the  muscle-fibres  are  active 
acts  on  their  part  depending  upon  whether  the  vaso-con- 
strictor or  the  vaso-dilator  fibres  are  stimulated.  It  is  true 
that  contraction  of  the  muscle-fibre  is  an  active  act  depend- 
ing on  stimulation  from  the  vaso-constrictors ;  but  were  this 
stimulus  removed  the  muscle-fibres  would  relax  and  the  artery 
dilate  passively,  owing  to  the  presence  of  blood  within  it. 

We  find  that  the  vaso-constrictors  act  continuously  with 
more  0r  less  intensity.  The  action  of  the  vaso-dilators  is 
only  occasionally  called  into  play,  when  marked  dilatation  of 
the  bloodvessels  is  called  for.  Also  the  dilators  do  not 
directly  act  upon  the  muscle-fibres,  causing  them  to  dilate ; 
but  act  upon  and  inhibit  the  action  of  the  vaso-constrictors, 
thus  allowing  a  passive  dilatation  of  the  arteries  because  the 
constrictor  action  is  removed. 

The  vaso-motor  centre  in  the  medulla  is  the  prime  centre, 
and  the  only  one  acting  during  normal  life.  The  secondary 
centres  in  the  cord  only  assume  control  if  the  primary  centre 
is  destroyed  or  its  connection  severed.  The  third  centres 


68  CIRCULATION  OF  THE  BLOOD. 

(close  to  the  artery)  only  act  if  the  secondary  centres  are  de- 
stroyed or  cut  off. 

Pulse. 

The  pulse  is  the  alternate  expansion  and  contraction  of  the 
artery  ("excursion  of  the  wall  of  the  artery  ")  resulting  from 
the  fresh  injection  of  blood  at  each  ventricular  systole.  Of 
course,  the  pulse-rate  is  the  same  as  the  number  of  heart- 
beats. 

A  number  of  various  terms  are  used  to  describe  the  char- 
acter of  the  pulse : 

Frequent  or  infrequent^=uumber  of  beats  per  minute  ; 
Regular  or  irregular —whether  beats  follow  successively  or 
not; 

Intermittent— beats  skipped  at  regular  intervals  ; 
Large  or  srnall=amplitude  of  excursion  of  wall  of  artery ; 
Quick  or  slow^whether  wall  of  artery  rises  rapidly  or  not. 
,ir.  (  are  synonymous  terms  ^ 

f  Ir-v'  denoting  a  high-ten-      Saseous>  ... 

IncompresS,ble,  i       g.          &        S  Their      «"P"*M«i 
Hard,  soft. 

^      opposites  are  J 

The  sphygmograph :  While  an  experienced  physician  can 
appreciate  slight  variations  in  the  character  of  the  pulse,  it 

FIG.  32. 


Marey's  sphygniograph  applied  to  the  arm  (Marey). 

is  only  by  means  of  the  graphic  method  that  the  different 
kinds  of  pulse  can  be  successfully  investigated  and  records 
kept.  The  sphygmograph  (Fig.  32)  is  an  instrument  which 


VENOUS  PULSE.  69 

measures  the  succession  of  the  alternate  dilatation  and  con- 
traction of  an  artery,  known  as  the  pulse ;  and,  magnifying 
these  movements,  registers  them  on  a  surface  moving  at  a 
uniform  rate  by  clockwork.  The  resultant  tracings  are  in 
the  form  of  a  wavy  line,  the  irregularities  of  which  show 
variations  of  the  pulse  too  slight  to  be  appreciated  by  the 
most  experienced  fingers  (Figs.  33  and  34). 


FIG.  33. 


Trace  of  the  radial  pulse,  taken  by  the  sphygmograph. 
FIG.  34. 


Dicrotic  pulse  of  typhoid  fever  (Marey). 


Extinction  of  pulse :  In  health  the  pulse  gradually  lessens 
as  we  get  further  from  the  heart,  and  is  entirely  lost  where 
the  arteries  break  up  into  capillaries.  There  is  no  pulse  in 
the  capillaries  nor  a  true  pulse  in  the  veins. 

Venous  pulse  :  Were  the  venous  walls  rigid,  there  would  be  a 
respiratory  pulse  in  the  veins.  In  deep  and  infrequent  respi- 
ration, as  in  partial  asphyxiation,  the  jugular  veins  may  be  seen 
to  be  distended  in  expiration  and  collapsed  during  inspiration, 
thus  forming  an  abnormal  venous  pulse.  The  cause  is  the 
pressure  of  the  atmosphere  upon  the  flaccid  vein,  it  being  easier 
to  empty  the  vein  than  to  fill  it  under  the  sudden  vacuum 
produced  by  the  act  of  inspiration  drawing  the  blood  from  the 
surface  veins  into  the  thorax.  The  veins  are  thus  emptied, 
and,  being  flaccid,  are  depressed  by  atmospheric  pressure. 

This  suction  power  of  the  inspiratory  vacuum  in  the  thorax 
extends  over  a  small  region  only  ;  roughly  speaking,  the  neck 
and  axilla.  This  is  the  so-called  "  dangerous  surgical  region ;" 
for  if  a  vein  is  punctured,  air  enters  the  blood-current  and 
is  carried  to  the  heart,  and  death  results.  But  the  flaccidity 


70  "CIRCULATION"   OF  THE  LYMPH. 

of  the  vein  naturally  causes  a  collapse  of  the  wall,  and  air 
will  not  rea< lily  enter  unless  the  wall  remains  ri^-id  from  arti- 
ficial or  abnormal  causes.  If  the  vein  can  collapse,  not  being 
held  open  by  connective  tissue  or  fascia,  or  artificially  or  as  a 
result  of  calcareous  infiltration,  no  air  will  be  allowed  to 
enter  the  vessel,  and  the  only  sign  will  be  an  expiratory  inter- 
mittent hemorrhage. 

"CIRCULATION"  OF  THE  LYMPH. 

The  lymphatics  :  The  blood-capillaries  as  they  pass  through 
the  various  tissues  of  the  body  are  surrounded  by  small  open 
spaces,  called  lymph-spaces.  These  spaces  are  the  interstices 
between  the  various  component  parts  of  the  body-tissues. 
The  lymph-spaces  form  the  open  mouths  of  microscopic 
lymph-capillaries,  that  closely  resemble  the  blood-capillaries 
in  structure.  The  lymph-capillaries  run  together  and  go  to 
form  larger  channels,  known  as  the  "lymphatics  n  «»r  "  lym- 
phatic vessels";  this  arrangement  is  comparable  to  the  for- 
mation of  veins  from  blood-capillaries  (Fig.  35).  These  lym- 
phatic vessels  converge  finally  into  two  main  channels- 
thoracic  duct  and  right  lymphatic  duct — that  pour  their  con- 
tents into  the  venous  system  at  the  junction  of  the  internal 
jugular  and  subclavian  veins  on  the  left  and  right  sides  of  the 
neck  respectively. 

The  lymphatic  radicles  (Fig.  36)  of  the  intestine,  although 
not  differing  in  structure  from  lymphatics  elsewhere  in  the 
body,  are  called  "  lacteals,"  because  of  the  milk-like  appear- 
ance of  the  lymph  they  contain. 

The  lymphatics  of  the  lower  extremities,  the  trunk  of  the 
body,  and  the  intestinal  tract,  go  to  form  a  long  channel,  the 
thoracic  duct,  which  ascends  along  the  front  of  the  vertebral 
column  1o  the  root  of  the  neck  on  the  left  side.  Here  the 
thoracic  duct  is  joined  by  lymphatics  draining  the  left  side  of 
the  head  and  left  upper  extremity.  The  combined  channel 
empties  into  the  left  innominate  vein  at  the  point  of  junction 
of  the  left  internal  jugular  and  left  snbelaviau  vein. 

The  lymphatics  of  the  right  side  of  the  head  and  right 
upper  extremity  join  to  form  the  rif/lit  lymphatic  duct — a  .-hort 


STOMATA  AND  PSEUDOSTOMATA. 


11 


structure,  one  and  a  half  inches  long,  emptying  into  the  right 
innominate  vein. 

Stomata  and  pseudostomata :  In  certain  parts  of  the  body 

FIG.  35.  Fro.  36. 


Lacteals  and  lymphatics,  during  digestion. 


Diagrammatic  representation 
of  the  origin  of  the  lacteals 
in  a  villus.  e,  central  lac- 
teal;  d,  lymph -channels; 
c,  columnar  epithelial  cells, 
the  attached  extremities  of 
which  are  directly  continu- 
ous with  the  lymph-chan- 
nels. 

there  have  been  found 
openings,  or  stomata,  by 
which  a  direct  communi- 
cation exists  between  the 
lymphatic  capillaries  and 
certain  cavities  previously 
supposed  to  be  entirely 
closed.  We  say  that 
absorption  takes  place 
through  pseudostomata 
when  fluids  pass  into  the 
lymphatic  system  through 
the  intercellular  cement- 
substance  of  the  epithe- 
lium or  endothelium 
covering  membranes. 


Stomata  have  been  found  in  the  peritoneum  and  pleura. 


72  "CIRCULATION"    OF  THE  LYMPH. 

Flow  of  lymph :  Thus  we  see  that  the  lymph  flows  from 
the  tissue-spaces  into  the  veins  at  the  root  of 
FIG.  37.  tjie  1R,ek  .  80  it  is  not  justifiable  to  speak  of 
the  "  circulation  of  the  lymph,"  as  there  is  no 
return-current.  The  lymph  is  formed  in  the 
lymph-radicles,  and  ceases  to  be  lymph  proper 
aV  soon  as  it  enters  the  venous  blood.  But 
new  lymph  is  constantly  formed,  and  so  there 
is  a  steady  onward  flow. 

Structure  of  lymphatics :  The  lymphatic 
channels  closely  resemble  the  veins  in  struct- 
ure, but  are  much  thinner  walled  and  pos- 
sess a  much  larger  number  of  valves  (Fig. 
37). 

Sources  of  lymph:  The  lymph  present  in 
the  lymph-spaces  is  made  up  of  the  exudation 
of  a  certain  amount  of  blood-plasma  through 
the  walls  of  the  capillaries,  together  with  the 
leukocytes  that  have  emigrated  from  the  capil- 
laries. It  is  probable  also  that  certain  por- 
tions of  the  body-tissues  may  be  found  in  the 
lymph,  which,  though  they  have  fulfilled  their 
functions  and  have  to  be  removed,  are  not 
entirely  waste-products.  They  may  be  capa- 
ble of  reorganization  in  the  lymph-glands  ;:nd 
Vphatic°sf(sSpplyr  may  be  absorbed  by  the  lymphatics  for  this 

purpose. 

The  lymph  in  the  radicles  of  the  intestines  is  composed  of 
the  blood-plasma  and  leukocytes  that  have  left  the  intestinal 
capillaries,  plus  an  innumerable  number  of  microscopic 
globules  of  fat  that  have  been  absorbed  from  the  digesting 
food.  These  particles  of  fat  render  the  lymph  milky  in 
appearance,  hence  the  name  "lacteals"  for  the  intestinal 
lymphatic  radicles.  This  milky  fluid  is  called  clii//c.  The 
lymph  proper  and  the  chyle  mingle  in  the  thoracic  duet  to  be 
poured  into  the  venous  system. 

I.i/nifili  IH'<>I><I-  is  a  pale  >t  raw-colored  fluid  ;  after  the  ad- 
mixture of  chyle  it  is  milky. 

Pressure  of  lymph :   The  blood  in    the   capillaries   has  been 


LYMPH-GANGLIA.  73 

stated  as  being  under  a  pressure  equal  to  20—50  mm.  of  mer- 
cury. In  exuding  through  the  capillary- walls  the  blood  loses 
about  one-half  its  pressure  ;  hence  we  find  that  the  lymph  in 
the  tissue-spaces  is  under  a  pressure  of  10—25  mm.  of  mer- 
cury. At  the  veins  of  the  neck  the  lymph  is  under  very  low 
pressure,  or  is  at  zero,  or  even  under  a  negative  pressure  due 
to  the  suction  of  the  chest. 

Factors  producing  lymph-flow;  In  some  of  the  lower  ani- 
mals there  is  a  distinct  separate  lymph-heart,  the  purpose  of 
which  is  to  act  as  a  force-pump  to  drive  on  the  lymph,  just 
as  the  human  heart  drives  on  the  blood.  In  man  there  is  no 
such  lymph-heart,  but  the  flow  of  lymph  depends  on  other 
causes.  They  are  as  follows : 

(1)  The  positive  pressure  (10—25  mm.  of  mercury)  in  the 
lymph-spaces,  as  opposed  to  the  zero  or  negative  pressure  at 
the  other  end  of  the  lymph-channel,  drives  the  lymph  on. 

(2)  The  muscular  movements  of  the  body  compressing  the 
lymphatics  force  the  lymph  on  in  the  proper  direction,  the 
reverse  flow  being  prevented  by  the  valves.     The  chyle  is 
aided  in  its  flow  by  the  actions  of  the  muscular  fibres  of 
the  small   intestine,  and   possibly  by  the  layer  of  unstriped 
muscle-fibre  found  in  each  intestinal  villus.     In  the  small  in- 
testine of  the  mouse  the  chyle  has  been  seen  to  flow  with 
intermittent   movements,    corresponding    to    the     peristaltic 
movements.     The  contractility  of  the   walls  of  the  lymph- 
vessels   themselves,  due  to   the    muscle-fibres  they   contain, 
probably  supplies  some  of  the  force. 

(3)  The  thoracic  aspiration   of   the   chest   on   inspiration 
sucks  on  the  lymph  in  the  same  manner  as  it  does  the  venous 
blood. 

Lymph-ganglia :  The  lymph-ganglia,  or  lymph-nodes,  are 
innumerable  small  masses,  varying  in  size  from  1  mm.  to  2 
cm.  in  diameter,  interposed  in  the  course  of  the  lymphatics. 
They  are  found  in  great  numbers  in  -the  neck,  thorax,  axilla, 
groin,  and  mesentery,  and  along  the  great  vessels  of  the  ab- 
domen. A  few  are  found  in  the  popliteal  space  and  in  the 
arm  as  far  as  the  elbow,  but  none  further  down  the  leg  or 
forearm. 

The  lymph-ganglia  consist  of  a  mass  of  cellular  pulp-sub- 


74 


"CIRCULATION"   OF  THE  LYMPH. 


Fro.  38. 


stance,  through  which   run  many  open  channels,  the  whole 
being  enclosed  in  a  capsule.     If  a  particular  lymph- vessel  be 

examined,  it  will  be  seen  to 
empty  directly  at  some  point 
into  a  lymph-ganglion.  The 
lymph  flows  through  the  open 
channels  in  the  substance  of 
the  ganglion  and  emerges  on 
the  opposite  side,  to  be  again 
collected  into  a  lymph-vessel, 
and  so  on  to  its  destination 
(Fig.  38). 

A  lymph-ganglion  is  com- 
parable to  a  sponge  placed  in  a 
snug-fitting  rubber  bag.  The 


cap- 
ics, 


Sim nle  lymphatic  gland,    a,  the  c 

suk',  with  sections  of  lymph;it 
<l,  (I,  conning  through  it;  b,  la- 
cunarand  intercommunicating  pas- 
sages, permeated  by  the  lymph,  and 
forming  the  superficial  lymph-paths 
nt'  Frry  ;  c,  nucleus  or  medullary 
p  >rtioii  of  the  gland,  in  the  centre 
of  which  the  section  of  a  bloodvessel 
may  be  seen.  The  path  pursued  by 
the  lymph  through  the  medullary 
portion  constitutes  the  deep  or  sec- 
ondary lymph-path  of  Frey  (Car- 
penter). 


rubber  bag  connects  on  one 
side  with  a  rubber  tube  repre- 
senting the  afferent  lymph- 
vessel,  and  from  the  opposite 
side  there  leads  away  from  the 
rubber  bag  another  tube  repre 
sc  11  ting  the  efferent  lymph- 
vessel.  The  rubber  bag  is  the 
representative  of  the  capsule  of  the  ganglion,  the  meshwork 
of  the  sponge  is  comparable  to  the  framework  of  the  ganglion, 
;s ml  the  holes  in  the  sponge  to  the  open  channels.  The  sub- 
stance of  a  lymphatic  ganglion  is  adenoid  tissue. 

Purpose  of  lymphatic  ganglia  :  The  lymphatic  ganglia  serve 
as  filters  for  the  lymph.  Also  the  cell-division  of  leukocytes 
occurs  in  their  channels.  An  important  attribute  is  the  way 
iu  which  they  serve  to  retard  the  spread  of  infection  through 
the  body,  thus  acting  as  safety-valves.  If  any  portion  of  the 
body  is  infected,  the  poison  is  carried  by  the  lymphatics  to 
their  especial  glands.  There  its  course  is  stopped  till  the 
opposition  of  the  glands  is  overcome,  when  it  proceeds  to 
the  next  ones.  As  a  result  of  this  we  uet  at  first  en- 
largement of  the  glands  ;  later,  if  the  process  continues, 
they  lireak  down  and  are  destroyed.  If  it  were  not  for 
their  action  in  this  way,  an  infected  wound  might  often 


MOVEMENTS  OF  RESPIRATION.  75 

prove  rapidly  fatal  before  surgical  treatment  had  time  to  be 
of  value. 

EESPIRATION. 

By  the  respiratory  act  we  mean  the  process  by  which  oxy- 
gen is  introduced  into  the  system  and  by  which  carbonic  ox- 
ide is  excreted.  This  function  is  performed  by  the  lungs,  and 
the  transfer  is  effected  by  the  agency  of  the  blood. 

The  respiratory  act  is  subdivided  into  (1)  the  "movements 
of  respiration,"  by  which  term  is  meant  those  movements  that 
cause  the  thorax  alternately  to  expand  and  collapse,  thus  fill- 
ing and  emptying  the  lungs  of  air ;  and  (2)  "  respiration  " 
used  to  designate  the  interchange  of  oxygen  and  carbon 
dioxide  between  the  blood  and  the  air  in  the  lungs  (external 
respiration) ;  also  the  exchange  of  oxygen  and  carbon  dioxide 
between  the  blood  and  the  tissues  of  the  body  (internal  respi- 
ration). 

Movements  of  respiration  :  The  action  by  which  the  lungs 
are  filled  with  air  (inspiration)  is  as  follows  :  The  thoracic 
cavity  is  expanded  by  muscular  action  ;  this  expansion  draws 
on  the  walls  of  the  lungs  through  the  intervention  of  the 
pleurae,  thus  enlarging  the  cavity  of  the  lungs.  To  prevent 
a  vacuum  in  the  lungs,  air  is  taken  through  the  nose  or  mouth, 
and  passes  through  the  pharynx  to  the  larynx  ;  entering  the 
rima  glottidis,  it  passes  through  the  larynx  to  the  trachea  and 
bronchi.  The  air  is  somewhat  warmed  and  moistened  in  its 
passage.  The  trachea  and  bronchi  are  lined  with  ciliated 
epithelium,  which  serves  to  sweep  particles  of  dust  and  the 
like  out  of  the  air-passages.  After  the  lungs  have  been  filled 
with  air  the  thoracic  wall  is  made  to  collapse  and  the  air  is 
expelled  from  the  lungs. 

The  respiratory  tract :  In  all  vertebrates  and  in  many  in- 
vertebrates certain  specialized  structures,  either  lungs  or  gills, 
are  specially  adapted  for  allowing  the  blood  to  come  into  close 
proximity  with  the  air  or  water  which  contains  air.  A  lung 
or  gill  in  its  simplest  form  consists  of  a  thin  membrane,  on 
one  side  of  which  is  a  network  of  thin-walled  bloodvessels, 
while  the  other  side  is  in  contact  with  the  air  or  water. 
There  is  a  difference  of  degree  only  between  the  most  com- 


76 


RESPIRATION. 


plex  and  the  simplest  forms.  In  man  the  respiratory  tract  is 
highly  complex,  and  includes  essentially  the  larynx,  trachea, 
bronchi,  and  lungs  (Fig.  39). 


FIG.  39. 


Human  larynx,  trachea,  bronchi,  and  lungs;   showing  the  ramification  of  the 
bronchi  and  the  division  of  the  lungs  into  lobules  (Dalton). 

The  larynx  :  The  air  enters  the  body  through  the  mouth  or 
nares.  It  first  passes  through  the  larynx,  the  upper  part  of 
tin-  respiratory  passage.  This  is  a  short  tube,  triangular  on 
section,  formed  of  hyaline  cartilage,  which  contains  the 
voral  cords.  At  its  lower  extremity  the  larynx  joins  the 
trachea. 

The  trachea :  The  trachea,  or  windpipe,  is  a  hollow  tube, 
four  to  four  and  a  half  inches  long,  composed  of  fibro-elas- 


MINUTE  ANATOMY  OF  THE  LUNG. 


77 


tic  membrane,  in  which  are  enclosed  a  series  of  from  sixteen 
to  twenty  cartilaginous  rings.  These  latter  serve  to  stiffen  it. 
At  its  lower  extremity  it  divides  into  two  bronchi,  one  for 
each  lung,  named  respectively  the  right  and  the  left. 

The  bronchi :  These  are  merely  smaller  editions  of  the 
trachea  and  of  a  similar  structure.  They  divide,  enter  the  sub- 
stance of  the  lungs,  and,  subdividing,  penetrate  every  part  till 
they  end  in  the  lobules.  As  they  get  smaller  the  walls 
become  thinner  and  the  cartilaginous  rings  disappear. 

The  lungs  :  These  occupy  the  larger  part  of  the  thorax. 
They  are  of  a  spongy,  elastic  texture,  and  on  section  appear 
to  be  solid  organs  for  the  greater  part.  In  reality  they  are 
hollow.  The  lungs  are  two  in  number,  the  right  and  the 
left,  of  which  the  former  is  partially  subdivided  into  three 
lobes  ;  the  latter  into  two. 

Covering  each  lung  separately  is  a  serous  membrane,  the 
pleura,  which  in  the  form  of  a  sac  envelops  the  outer  sur- 

FIG.  40. 


Diagrammatic  view  of  the  pleural  sacs  with  the  heart  and  lungs  interposed.    A,  in- 
ternal mammary  artery  ;  N,  phrenic  nerve. 

face  of  the  lung  and  the  inner  surface  of  the  chest-wall.  The 
pericardium  containing  the  heart  is  interposed  between  the 
two  lungs  (Fig.  40). 

Minute   anatomy  of   the  lung :  Each  lobe  of  the  lung  is 


78  RESPIRATION. 

composed  of  numerous  lobules,  into  each  of  which  a  small 
bronchiole  enters,  and  the  minute  terminal  branches  of  these 
bronchioles  (infimdibula]  widen  into  a  .sort  of  irregular  funnel 
having  pouched  or  sacculated  dilatations,  known  as  air-cc//*. 
These  air-cells  are  supported  by  numerous  elastic  fibres,  and 
are  lined  with  a  very  thin  layer  of  flat  (not  ciliated)  epi- 
thelium. Outside  the  epithelial  lining  is  a  very  close  mesh 
of  capillaries,  which  are  often  exposed  to  air  on  both  sides  In- 
lying in  a  partition  between  two  of  the  air-cells.  The  air- 
cells  or  vesicles  are  about  one-sixtieth  of  an  inch  in  diameter, 
and  the  space  between  the  capillaries  is  often  less  than  the 
diameter  of  a  capillary  (Figs.  41  and  42).  The  total  surface 
in  the  lungs  bathed  by  the  air  is  about  two  hundred  square 
metres. 

FK;.  41.  FIG.  42. 


Single  lohule  of  human  lung,    a,  ulti-      Network  of  capillary  blood-vossi-ls  in  the 

mate  bronchial  tube;  h,  cavity  of  pulmonary   vesicles    «.f   thr    hone,     n 

:>bule;  c,, c,  c,  pulmonary  cells,  or  cavity  of  vesicle,  with  capillary  plexus  : 

vesicles  (Dalton).  ft,  pulmonary  blood-vesaels,  supplying 

capillary  plexus  (Frey). 

Muscles  of  inspiration:  During  <|iiiet  inspiration  the  cavity 
of  the  chest  is  increased  in  all  three  diameters — vertical, 
anter«i-jM)>trri«.r,  and  lateral.  The  upper  part  of  the  thoracic 
ba-Ui-t  being  fixed,  the  vertical  diameter  is  increased  by  the 
d'-mit  of  the  diaphragm  in  contracting  (  Fig.  4:5).  Th<>  ex- 
ternal intercostals,  together  with  other  muscles,  act  on  the 


MUSCLES  OF  INSPIRATION, 


79 


ribs  so  that  they  turn  on  their  axes,  with  the  result  that  the 
sternal  ends  are  raised  up  and  carried  forward  ;  at  the  same 
time  the  peculiar  curve  that  exists  in  the  rib  at  its  angle 

FIG.  43. 


TT 


Si 


A 


Diagrammatic  sections  of  the  body  in  inspiration  and  expiration.  A,  inspiration; 
B,  expiration ;  Tr,  trachea ;  St,  sternum ;  D,  diaphragm ;  Ab,  abdominal 
walls.  The  shading  roughly  indicates  the  stationary  air  (Huxley). 

causes  an  eversion  of  the  lateral  aspect  of  the  rib  when  the 
sternal  end  is  brought  upward  and  forward.  This  eversion 
increases  the  lateral  diameter. 

The  axis  of  a  rib  is  a  line  running  through  the  centre  of 
the  head  (vertebral  end)  of  the  rib  and  through  the  articula- 
tion of  the  rib  with  the  transverse  process  of  the  vertebra. 

The  muscles  producing  these  changes  in  the  diameters  of 
the  chest  are  the  muscles  of  "  quiet  inspiration/'  and  are  as 
follows : 

Diaphragm  increases  the  vertical  diameter  • 


80 


RESPIRATION. 


Scaleni  fix  upper  part  of  the  thorax ; 
External  intercostals  ] 

and  >  draw  the  ribs  upward  ; 

Interchondrals  J 

C  fix   the   second  rib  and   raise 
Serrati  postici    stiperiores<       the  third,  fourth,  and  fifth 

(      ribs; 
Levatores  costarum  breves  raise  the  upper  ten  ribs. 

It  is  stated  that  of  the  two  types  of  respiration,  "  thoracic  " 
and  "  abdominal/'  the  former  is  more  marked  in  women  and 
the  latter  in  men.  This  is  true  in  the  sense  that  women  in- 
crease the  antero-posterior  and  the  lateral  diameter  of  the 
chest  more  than  do  men,  owing  to  the  functional  differences 
between  the  sexes,  and  also  due  to  habits  of  dress,  etc.  On 


FIG.  44. 


FIG.  45. 


The  changes  of  the  thoracic  and  abdominal    The  same  in  the  female  (Hutchinson). 
walls  of  the  male  during  respiration. 

tin1  other  hand,  adult  males  and  children  of  both  sexes  use 
tin-  diaphragm  almost  exclusively  in  quiet  inspiration  (Fiir>. 
44  and  45). 


MUSCLES  OF  EXPIRATION.  81 

During  forced  inspiration  additional  muscles  are  brought 
into  play  to  permit  of  a  more  powerful  inspiratory  act.  Be- 
side the  muscles  already  enumerated,  the  muscles  of  forced 
inspiration  are  as  follows  : 

Trapezei  and  rhomboidei  fix  the  shoulders ; 

Pectorales  majores  and  minores,  acting  from  the  fixed 
shoulders,  draw  the  sternum  and  ribs  upward ; 

Sterno-mastoidei  fix  the  upper  part  of  the  chest ; 

Erector  sphue  stiffen  the  vertebral  column ; 

Serrati  postici  inferiores.  ^   ^  -IT 

QuadJi  lu.bo,,™,          U«  a-k^rt-  Downward 

oacro-lum  bales,  ) 

Muscles  of  expiration :  At  the  close  of  inspiration  the  va- 
rious muscles  that  raised  the  thorax  relax,  and  by  its  own 
weight  the  thorax  drops,  thus  compressing  the  lungs  and  ex- 
pelling the  air.  In  addition  there  is  an  active  collapse  of 
the  lungs  due  to  the  recoil  of  the  elastic  tissue  in  the  sub- 
stance of  the  lung,  the  elastic  fibres  having  been  put  on  the 
stretch  during  inspiration.  Also  during  inspiration  the  inter- 
osseous  portions  of  the  internal  intercostal  muscles  were  put 
upon  the  stretch ;  when  expiration  begins  these  muscles  con- 
tract, but  their  contraction  is  not  sufficiently  forcible  to  pull 
the  ribs  down,  and  the  only  purpose  of  this  contraction  seems 
to  be  to  keep  the  intercostal  tissues  tense  and  thus  prevent 
bulging  of  the  intercostal  spaces. 

Also  during  inspiration  each  costal  cartilage  was  twisted 
in  the  direction  of  its  long  axis,  due  to  the  eversion  of  the  rib 
twisting  the  rib-end  of  the  cartilage,  the  sternal  end  being 
fixed.  During  expiration  the  costal  cartilage  tends  to  un- 
twist itself.  So  we  may  justly  say  there  are  no  muscles  for 
quiet  expiration,  as  the  act  is  performed  by  the  weight  of  the 
thorax,  elastic  recoil  of  the  lungs,  and  untwisting  of  the 
cartilage. 

Forced  expiration  is  accomplished  by  the  intervention  of 
many  muscles  as  follows  : 

Interosseous  internal  intercostals  act  forcibly  in  drawing 
down  the  ribs,  when  the  lower  part  of  the  thorax  is  fixed ; 

Abdominal  muscles  fix  the  lower  part  of  the  thorax  and 
press  the  abdominal  contents  upward; 

6— Phys. 


82  RESPIRATION. 

Levatores  ani  and  perineal  muscles,  hold  the  floor  of  the 
pelvis  rigid  against  abdominal  pressure. 

Triangtilaris  sterni  draws  the  costal  cartilages  down. 

Frequency  of  respiration :  In  normal  adult  life,  with  the  body 
in  repose,  there  are  about  eighteen  respiratory  cycles  to  the 
minute.  Inspiration  and  expiration  alternate  without  any 
appreciable  pause  between  the  two.  The  inspiration  is  some- 
what shorter  than  the  expiration  ;  the  ratio  being  about  5  to 
6.  In  infants  and  invalids  the  rate  is  often  much  more  rapid. 
The  ratio  to  the  pulse-rate  is  about  1  to  4  in  the  healthy  in- 
dividual. During  violent  activity  both  the  respiratory-  and 
pulse-rates  increase,  but  the  ratio  remains  about  the  same. 

Respiratory  sounds  :  When  the  ear  is  placed  in  contact  with 
the  chest-wall,  or  a  stethoscope  is  used,  a  respiratory  murmur 
will  be  heard,  fairly  marked  during  inspiration ;  short  and 
faint  during  expiration,  in  a  healthy  subject.  It  varies  in 
diiferent  parts  of  the  chest-wall,  being  loudest  over  the  large 
bronchi.  The  changes  in  these  murmurs  incident  to  disease 
of  the  respiratory  tract  are  just  as  characteristic  of  the  differ- 
ent pathological  processes  as  are  changes  in  the  heart- sounds 
depending  on  disease  of  the  heart ;  and  it  is  upon  the  recog- 
nition of  these  changes  that  the  value  of  auscultation  depends. 

Associated  respiratory  movements :  With  every  inspiration 
(especially  if  rapid)  there  is  dilatation  of  the  nostrils;  and  a 
partial  closure  during  expiration.  The  rima  glottidis  is  in 
the  same  way  opened  for  the  ingress  of  air.  This  is  like  the 
respiratory  act,  in  that  the  opening  is  a  muscular  act  during 
inspiration,  and  the  recoil,  elastic,  in  ordinary  breathing. 

Capacity  of  the  lungs:  The  lungs,  if  filled  to  their  utmost, 
can  hold  about  4500  c.c.  of  air.  This  total  of  air  is  divided 
as  follows:  (1)  tidal  air,  (2)  reserve  air,  (3)  residual  air,  and 
(4)  complementary  air. 

Tidal  air  is  the  ordinary  amount  of  air  that  passes  in  and 
<>ut  during  each  quiet  respiration.  It  seldom  goes  lower  than 
the  large  bronchi.  Its  amount  is  500  c.c. 

Reserve  air  is  the  amount  of  air  in  addition  to  the  tidal  air 
one  can  expel  from  the  lungs  in  a  forced  expiration.  It  is 
ordinarily  lodged  in  the  bronchi  and  bronchioles.  Its  amount 
is  1600  c.c. 


EXPIRED  AIR.  83 

Residual  air  is  found  in  the  alveoli  of  the  lungs,  and  remains 
even  after  the  most  violent  expirations.  Amount,  800  c.c. 

Complementary  air  is  the  air  taken  in,  in  addition  to  the 
tidal  air,  in  the  most  forced  inspiration.  Amount,  1600  c.c. 

The  complementary,  tidal,  and  reserve  airs  have  been 
called  the  vital  capacity  of  the  lungs. 

Force  of  the  inspiratory  and  expiratory  muscles :  The  force 
of  the  inspiratory  muscles  is  greatest  in  people  of  about  five 
feet  seven  and  a  half  inches  in  height,  being  equivalent,  on 
the  average,  to  a  column  of  mercury  three  inches  high.  It 
diminishes  in  people  above  and  below  this  height.  The  force 
of  expiration  is  about  one-third  greater;  but  the  variations 
are  not  so  regular,  as  there  are  many  variations  due  to  the 
fact  that  the  expiratory  muscles  are  used  for  other  purposes, 
hence  becoming  stronger. 

Composition  of  inspired  air :  Pure  air  has  a  nearly  uniform 
composition : 

By  volume.  By  weight. 

Nitrogen, 79  parts         75  parts 

Oxygen, 21      "  25      " 

Carbonic  acid, 04  part 

Ammonia  and  impurities,  trace. 

Expired  air :  After  its  sojourn  in  the  lungs  there  are 
marked  changes  in  the  respired  air.  Its  temperature  is 
changed  to  nearly  that  of  the  body,  regardless  of  the  tempera- 
ture of  the  atmosphere.  The  oxygen  is  decreased,  carbon 
dioxide  and  aqueous  vapor  are  increased ;  also  there  are 
present  many  minute  particles  of  volatile  organic  bodies. 
Nitrogen  is  unchanged.  The  composition  of  expired  air  is 
about  as  follows : 

By  volume. 

Nitrogen, 79  parts 

Oxygen, 16      " 

Carbon  dioxide, 4      " 

Water  increased  (from  6  to  30  ounces  per  day). 
Volatile  organic  bodies  are  added. 

The  total  weight  of  expired  air  is  somewhat  heavier  than 


84  RESPIRATION. 

that  of  inspired  air,  because  the  amount  of  carbon  dioxide 
gained  weighs  more  than  the  amount  of  oxygen  lost. 

In  temperate  atmospheres  the  volume  of  expired  air  is 
greater  than  that  of  the  inspired  air,  because  the  air  has  been 
expanded  by  being  heated.  If,  however,  the  expired  air  lie 
reduced  to  the  temperature  of  that  inspired,  the  volume  of 
expired  air  will  be  found  less  than  that  inspired,  as  the  car- 
bon dioxide  gained  is  less  bulky  than  the  oxygen  lost. 

Value  of  nitrogen:  The  nitrogen  in  the  atmosphere  serves 
merely  as  a  diluent ;  pure  oxygen  would  be  too  powerful  to 
serve  for  respiration.  We  do  find  a  little  nitrogen  in  solu- 
tion in  the  blood-plasma,  but  it  probably  serves  no  purpose 
in  the  body  economy. 

External  respiration :  By  external  respiration  is  meant  the 
interchange  of  gases  in  the  respired  air  and  the  gases  of  the 
blood  while  in  the  pulmonary  capillaries.  It  is  true  the 
ordinary  tidal  air  of  respiration,  lodged  as  it  is  in  the  upper 
air-passages,  does  not  come  into  actual  contact  with  the  pul- 
monary capillaries,  but  by  virtue  of  the  physical  laws  of  diffu- 
sion of  gases  the  oxygen  in  the  tidal  air  is  diffused  into  the 
reserve  air,  and  carbon  dioxide  and  other  wastes  of  the  re- 
serve air  are  diffused  into  the  tidal  air.  A  similar  exchange 
takes  place  between  the  reserve  air  and  the  residual  air. 
Thus  it  comes  about  that  the  residual  air,  while  never  leaving 
the  air-cells  of  the  lungs,  is  constantly  revivified  with  fresh 
oxygen  and  constantly  gets  rid  of  its  carbon  dioxide  and 
other  impurities.  The  blood  coming  to  the  pulmonary  capil- 
laries through  the  pulmonary  arteries  is  rich  in  carbon  diox- 
ide and  other  wastes,  but  poor  in  oxygen  ;  on  the  other  hand, 
the  air  in  the  alveoli  is  rich  in  oxygen,  but  poor  in  carbon 
dioxide.  Hence  the  oxygen  in  the  air  is  under  high  tension 
as  compared  with  the  oxygen  in  the  blood;  and  likewise  the 
carbon  dioxide  of  the  blood  is  under  higher  tension  than  the 
carbon  dioxide  of  the  air.  Owing  to  these  ditlcivnces  in 
pressures,  interchanges  of  the  gases  readily  take  place,  so  as 
to  equal i/e  the  pressures. 

In  the  blood  oxygen  is  in  loose  chemical  combination  with 
the  haemoglobin  (<>x\ -h  \  moglobin).  The  amount  of  oxygen 
in  the  residual  air  of  the  pulmonary  alveoli  is  estimated  at 


NERVOUS  MECHANISM  OF  RESPIRATION.  85 

about  10  per  cent.,  that  of  expired  air  being  16  per  cent.  It 
is  found  that  unless  there  is  present  about  4  per  cent,  of  oxy- 
gen there  is  no  tendency  for  the  blood  of  the  pulmonary 
arteries  (venous)  to  take  up  fresh  oxygen ;  or,  the  tension  of 
the  oxygen  in  the  reduced  hemoglobin  of  venous  blood  is 
about  4  per  cent.,  and  unless  the  oxygen-tension  in  the  lungs 
is  greater  there  is  no  absorption  of  oxygen.  But,  as  we  have 
seen,  the  amount  of  oxygen  amounts  to  at  least  10  per  cent., 
and  therefore  the  excess  is  sufficient  to  exceed  the  demands, 
and  the  exchange  is  readily  made  by  diffusion  through  the 
thin  capillary  walls  of  the  alveoli.  On  the  other  hand,  the 
tension  of  the  carbonic  acid  in  the  pulmonary  arteries  is  much 
higher  than  in  the  alveoli,  and  hence  the  extrusion  of  this  gas 
by  diffusion  is  accomplished. 

The  following  changes  in  the  blood  are  noted  after  passing 
through  the  pulmonary  capillaries  :  (1)  Color,  deep  purple  to 
bright  scarlet  by  oxidization  of  the  reduced  haemoglobin — 
i.  e.,  from  venous  becoming  arterial  blood  ;  (2)  gains  oxygen ; 
(3)  loses  carbonic  acid  ;  (4)  becomes  cooler ;  (5)  coagulates 
more  readily. 

Internal  respiration :  Internal  respiration  means  the  ex- 
change of  gases  between  the  arterial  blood  and  the  tissues  of 
the  body.  This  interchange  takes  place  through  the  walls 
of  the  systemic  capillaries,  and  depends  on  the  same  physical 
laws  (differences  in  pressure)  as  already  described  for  the 
pulmonary  exchange. 

The  arterial  blood,  rich  in  oxygen,  gives  oxygen  to  the 
needy  tissues,  and  in  return  relieves  the  tissues  of  their 
burden  of  carbon  dioxide  and  other  wastes.  In  the  systemic 
capillaries  the  blood  changes  from  arterial  to  venous. 

Nervous  mechanism  of  respiration  :  Respiration  is  described 
as  one  of  the  so-called  automatic  acts,  but  is  profoundly  modi- 
fied by  the  reflexes  and  partially  controlled  by  the  will. 

Throughout  our  lives  we  continue  to  breathe  unconscious 
of  the  fact,  unless  our  attention  is  called  to  it.  A  dash  of 
cold  water  on  the  skin  or  a  disagreeable  mental  or  visual  pict- 
ure will  produce  an  uncontrollable  gasp  ;  these  are  examples 
of  reflex  influences  on  respiration.  One  may  so  exert  will  as 
to  increase  or  decrease  the  rate  of  respiration,  but  only  up  to 


86  RESPIRATION. 

certain  limits.  It  is  impossible  to  commit  suicide  by  "  hold- 
ing the  breath." 

Centres  for  respiration  :  In  the  medulla  oblongata  arc  cen- 
tres for  each  half  of  the  body,  from  which  arise  automatically 
the  rhythmical  impulses  for  the  inspiratory  act*.  These  so- 
called  automatic  impulses  are  generated  by  the  presence  or 
absence  of  oxygen  in  the  blood  (not  presence  of  carbon 
dioxide)  bathing  the  medulla.  If  the  blood  in  the  medulla 
is  rich  in  oxygen,  there  is  no  impulse  for  an  inspiratory  act ; 
but  as  soon  as  the  oxygen  is  diminished  to  a  given  point  the 
respiratory  centre  is  stimulated  to  make  an  inspiratory  effort. 
The  nerves  which  convey  to  the  muscles  of  inspiration  their 
impulse  are  the  phrenics  (to  the  diaphragm)  and  the  intercos- 
tals  (to  the  intercostal  muscles).  In  addition  to  the  auto- 
matic impulses  from  the  centres,  there  are  certain  regular 
reflex  impulses  (other  than  the  unusual  ones  mentioned 
above — cutaneous  reflexes,  etc.)  that  are  conveyed  to  the 
centres  by  the  pneumogastric  nerves. 

The  pneumogastric  nerves  arising  in  the  medulla  scud 
branches  to  the  lungs  that  terminate  in  filaments  distributed 
to  the  walls  of  the  air-cells.  These  fibres  are  afferent,  and 
are  stimulated  by  two  factors  :  (1)  The  lack  of  oxygen  in  the 
air  of  the  alveoli  after  expiration  ;  (2)  During  the  partial  col- 
lapse of  the  lung  at  the  end  of  expiration  these  filaments  are 
mechanically  pinched  by  the  walls  of  the  air-cells. 

The  stimuli  thus  generated  in  the  terminal  filaments  of  the 
pulmonary  branches  of  the  pneumogastric  nerves  convey 
their  impulses  to  the  centres  of  respiration,  producing  an  ad- 
ditional impulse  for  inspiration. 

The  condition  (amount  of  oxygen)  of  the  blood  bathing  the 
respiratory  centre  is,  however,  the  prime  factor,  the  afferent 
impulses  of  the  pneumogastrics  being  only  secondary. 

While  there  are  distinct  expiratory  centres  in  the  me- 
dulla for  expiration,  they  act  to  produce  forced  expiration 
only  when  properly  stimulated  by  afferent  nerves — as,  for 
example,  if  the  superior  laryngeal  nerve  be  stimulated,  the 
result  is  a  forced  explosive  expiration,  or  cough. 

Under  <>/-(f innri/  oircurngtance*  when  the  inspiratory  act  is 
accomplished,  the  condition  of  the  blood  no  longer  calls  for 


SECTION  OF  VAGI.  87 

more  oxygen,  and,  the  inspiratory  impulse  ceasing,  the  mus- 
cles of  inspiration  relax  and  expiration  is  a  purely  passive 
act. 

In  dyspnoea,  however,  the  expiratory  centres  are  stimu- 
lated. 

Synchronism  of  respiratory  centres  :  Although  there  is  a 
respiratory  centre  for  each  half  of  the  body,  nevertheless, 
owing  to  their  association-fibres,  the  two  centres  work  syn- 
chronously. By  making  a  median  section  of  the  medulla,  the 
centres  are  disassociated,  so  that,  if  proper  artificial  stimuli  be 
applied,  one  half  of  the  chest  may  be  made  to  inspire,  while 
the  other  half  expires. 

Lack  of  oxygen  in  the  blood  :  If  the  need  be  only  moderate, 
there  will  be  increased  effort  of  both  expiration  and  inspira- 
tion, and  the  respirations  will  be  rapid — a  condition  known 
as  hyperpnoea.  As  the  oxygen  becomes  less  and  less  abundant 
the  symptoms  become  more  severe,  and  the  condition  is  known 
as  dyspnoea.  The  dyspnoea  increasing,  the  respiratory  efforts 
become  very  violent,  and  the  condition  of  asphyxia  is  seen. 
In  this  the  face  is  blue,  eyes  staring,  face  anxious,  and  respir- 
ations very  rapid  and  strident.  Then  follows  a  convulsive 
condition  which  is  brief,  the  convulsions  being  very  violent 
and  involving  the  whole  body.  After  this  the  patient  lapses 
into  a  state  of  exhaustion,  in  which  the  respirations  are  slow 
and  very  feeble,  and  the  general  condition  is  one  of  collapse. 
Death  ensues  very  soon. 

Apncea  is  absence  of  breathing. 

Section  of  vagi :  If  one  pneurnogastric  nerve  be  divided 
below  the  offshoot  of  the  inferior  laryngeal  nerve,  there  is  a 
temporary  excitation  of  the  respiratory  rate,  due  to  the  mechan- 
ical stimulus  of  cutting ;  but  soon  the  respirations  return  to 
normal,  .the  other  vagus  taking  up  the  work  of  both. 

If  both  vagi  be  divided  below  the  inferior  laryngeal  nerve, 
there  is  an  excitation  of  respiration  due  to  the  stimulus  of 
cutting,  soon  followed  by  slower  and  deeper  inspirations  and 
active  expirations.  Stimulation  of  the  central  ends  of  cut  vagi 
will  bring  the  rate  and  character  back  to  the  normal. 

If  the  superior  laryngeals  be  divided,  a  cough  or  expiratory 
sniff  follows  the  act  of  cutting ;  later  on  the  subject  dies  of 


88  RESPIRATION. 

'•  foreign-body  pneumonia,"  because  the  sensation  of  the  lar- 
VMX  being  lost  foreign  particles  pass  the.  larynx  without  being 
coughed  out,  enter  the  lungs,  and  give  rise  to  a  fatal  pneu- 
monia. 

Section  of  the  inferior  laryngeals  gives  the  same  result ;  for 
although  sensations  in  the  larynx  are  present  if  the  superior 
laryngeals  are  intact,  all  motion  in  the  larynx  is  lost  and 
coughing  is  ineffectual. 

Vitiated  atmosphere :  In  ill-ventilated  rooms  the  air  of  the 
room  is  used  repeatedly,  and,  besides  becoming  partial!}  de- 
prived of  its  oxygen,  is  charged  with  carbonic  acid  and  with 
putrescible  nitrogenous  organic  matters.  This  gives  rise  to  an 
atmosphere  which  is  intolerable  to  one  who  enters  from  fresh 
air.  That  such  a  condition  is  unsanitary  needs  no  argument. 
The  mere  presence  of  the  excess  of  carbonic  acid  is  not  in 
itself  injurious;  but  the  amount  of  carbon  dioxide  is  indica- 
tive of  the  amount  of  organic  matter  present,  and  it  is  the 
latter  that  are  highly  poisonous.  It  is  generally  accepted  as 
a  fact  that  about  1000  cubic  feet  of  air-space  per  head  must 
be  allowed  in  sleeping-quarters,  and  sufficient  facilities  for 
exchange  of  air  to  allow  complete  change  in  each  hour.  This 
ventilation  must  be  accomplished  without  exposure  to 
draughts. 

Effect  of  respiration  on  the  circulation :  As  the  heart  and  its 
great  vessels  are  contained  together  with  the  lungs  in  the 
thorax,  an  air-tight  cavity,  there  naturally  results  a  certain 
alteration  in  pressure  on  the  heart  when  the  capacity  of  the 
thorax  changes.  Though  the  expansion  of  the  lungs  during 
inspiration  tends  to  compensate  for  this  increased  capacity,  it 
never  does  so  fully,  as  part  of  the  atmospheric  pressure  is 
expended  in  overcoming  the  elasticity  of  the  lungs.  There- 
fore, during  inspiration  the  pressure  on  the  heart  become.- 
considerably  less  than  the  atmospheric  pressure  exerted  on 
the  bloodvessels  outside  of  the  thoracic  cavity.  This  differ- 
ence varies  from  5  to  8  mm.  of  mercury  during  the  pause, 
up  to  25  or  30  mm.  at  the  end  of  a  deep  inspiration.  The 
result  of  this  is  to  draw  more  blood  through  the  veins  into 
the  heart  during  inspiration,  and  consequently  to  increase  ar- 
terial tension.  The  relative  values  of  intrathoracic  press- 


SPECIAL  RESPIRATORY  ACTS. 


89 


ure  and  arterial  tension  may  be  graphically  expressed  as  in 
Fig.  46. 

Special  respiratory  acts :  There  are  a  number  of  involun- 
tary and  voluntary  special  respiratory  acts,  largely  reflex, 
which  are  dependent  upon  modifications  of  inspiration  and 

FIG.  46. 

i  e  i 


J 


Comparison  of  blood-pressure  curve  with  curve  of  intrathoracic  pressure.  To  be 
read  from  left  to  right,  a  is  the  blood-pressure  curve,  with  its  respiratory  undu- 
lations, the  slower  beats  on  the  descent  being  very  marked ;  bis  the  curve  of 
intrathoracic  pressure  obtained  by  connecting  one  limb  of  a  manometer  with 
the  pleura!  cavity.  Inspiration  begins  at  i,  expirati9n  at  e.  The  intrathoracic 
pressure  rises  very  rapidly  after  the  cessation  of  the  inspiratory  effort,  and  then 
slowly  falls  as  the  air  issues  from  the  chest ;  at  the  beginning  of  the  inspiratory 
effort  the  fall  becomes  more  rapid  (Foster). 

expiration — e.  g.,  sighing,  hiccough,  cough,  sneezing,  speaking, 
singing,  sniffing,  sobbing,  laughing,  yawning. 

Sighing :  This  results  from  a  prolonged  inspiration,  the  air 
passing  noiselessly  through  the  larynx  and  being  rather  sud- 
denly expelled. 

Hiccough:  This  resembles  sighing,  but  the  inspiration  is 
sudden,  due  to  spasmodic  action  of  the  diaphragm. 

Cough :  This  results  from  a  deep  inspiration  followed  by  a 
forced  and  sudden  expiration,  during  which  the  glottis  is 
momentarily  closed  by  spasmodic  action  of  the  vocal  cords. 

Sneezing :  In  this  case,  following  on  a  deep  inspiration,  by 
a  sudden  and  forced  expiration  the  air  is  directed  through  the 
nasal  passages. 

Speaking :  In  this  case  there  is  a  voluntary  expiration,  and 
the  vocal  cords,  being  rendered  tense  by  their  muscles,  vibrate 
as  the  air  passes  over  them,  producing  sound. 


90  DIGESTION. 

Singing :  This  only  varies  from  speaking  in  the  differing 
tension  and  position  of  the  vocal  cords  and  the  consequently 
different  sounds  produced, 

Sniffing:  This  results  from  rapidly  repeated  but  incom- 
plete nasal  inspirations. 

Snhltiny:  This  consists  of  a  series  of  convulsive  inspira- 
tions, during  which  the  glottis  is  more  or  less  closed. 

Laughing:  This  results  from  a  series  of  short  and  rapid 
expirations. 

Yawning :  This  is  an  act  of  inspiration,  more  or  less  in- 
voluntary, accompanied  by  a  stretching  of  various  facial 
muscles. 

Sucking:  This  is  not  really  a  respiratory  act.  It  is  caused 
chiefly  by  the  depressor  muscle  of  the  os  hyoides,  which,  by 
drawing  down  and  back  the  floor  of  the  mouth,  produce  a 
partial  vacuum  in  it. 

DIGESTION. 

By  digestion  we  indicate  the  process  by  which  food  is  in- 
troduced into  the  body  and  prepared  in  such  way  that  it 
becomes  suitable  for  absorption  and  tissue-nutrition.  The 
process  may  be  divided  logically  and  conveniently  into  masti- 
cation, insalivation,  deglutition,  stomach  digestion,  intestinal 
digestion,  and  defecation. 

The  mouth :  The  first  portion  of  the  alimentary  tract  is  the 
mouth.  In  this  is  received  the  food  destined  to  support  the 
body.  It  is  a  cavity  contained  between  the  jaws  and  bounded 
laterally  by  the  cheeks.  Its  roof  is  formed  by  the  hard  and 
soft  palate,  and  its  floor  by  the  tongue.  It  is  lined  through- 
out with  mucous  membrane,  which  is  provided  with  numer- 
ous mucous  glands,  and  into  it  open  the  ducts  of  the  salivary 
glands.  The  tongue  is  both  a  prehensile  organ  and  also  the 
chief  seat  of  the  sensation  of  taste.  In  this  cavity  occurs  the 
process  of  mastication. 

Mastication :  When  a  mass  of  food  enters  the  mouth  it  is 
caught  by  the  tongue  and  moved  to  a  position  such  that  it 
may  he  erushed  and  ground  between  the  upper  and  lower 
teeth.  This  process  is  favored  by  the  action  of  the  tongue 
and  of  the  cheeks,  which  not  only  crush  the  softer  food- 


MASTICATION. 


91 


masses,  but  bring  the  less  tractable  portions  repeatedly  under 
the  action  of  the  teeth. 

There  are  during  life  two  sets  of  teeth,  temporary  and  per- 
manent. In  the  first  set  are  twenty  teeth ,  and  in  the  second 
thirty-two.  The  permanent  set  are  arranged  as  follows  : 


Upper. 

Lower. 


Molar.      Bicuspid.     Canine.      Incisor.    Canine.     Bicuspid.      Molar. 
3214123 


A  tooth  may  be  roughly  described  as  consisting  of  a  crown, 
neck,  and  fang  or  fangs.  The  crown  is  the  portion  which  pro- 
jects above  the  margin  of  the  gum  ;  the  neck  is  the  con- 
stricted part  below  the  crown  which  is  covered  by  the  free 


FIG.  47. 


Section  of  human  molar  tooth,  magnified  (Owen). 

edges  of  the  gum  ;  while  the  fang  or  root  includes  all  below 
this.  On  making  a  section  of  a  tooth,  for  instance  a  molar 
(Fig.  47),  it  will  be  seen  that  there  is  a  cavity  within  the 


92  DIGESTION. 

crown  which  extends  into  and  through  the  fangs,  opening  by 
a  small  aperture  at  their  apices.  This  is  the  pu/jt-rdrify,  and 
contains  in  the  living  tooth  the  pulp.  A  portion  of  the  tooth- 
structure  resembles  bone,  anatomically  as  well  as  chemically. 
The  crusta  petrosa,  or  cement,  is  true  bone,  and  covers  in  the 
<!<  ntine  of  the  fang,  while  outside  the  dentine  of  the  crown  is 
a  very  dense  layer  of  enamel  (of  epithelial  origin). 

Muscles  of  mastication  :  Biting  movements  are  produced  by 
the  action  of  the  temporal,  masseter,  and  internal  pterygoid 
muscles,  opposing  the  depressors  of  the  jaw  ;  grinding  move- 
ments are  produced  by  the  alternate  action  of  the  external 
pterygoids.  The  action  is  to  some  extent  reflex,  though  largely 
voluntary,  and  is  controlled  in  the  medulla  through  branches 
of  the  cranial  nerves,  motor  impulses  coming  through  branches 
of  the  trigeminus  and  (to  the  tongue)  hypoglossal  nerves. 

Insalivation  :  The  mixing  and  thorough  moistening  of  the 
food-mass  with  the  saliva  and  mucus  in  the  mouth  during  the 
act  of  chewing  are  called  insalivation. 

Saliva:  The  saliva  is  derived  almost  entirely  from  the 
parotid,  submaxillary,  and  sublingual  glands,  and  is  secreted 
most  abundantly  during  the  mastication  of  food.  Of  the 
glands,  the  parotid  secretes  pure  saliva  containing  ptyalin ;  the 
sublingual  secretes  only  mucus  ;  while  the  submaxillary  is  a 
mixed  gland,  secreting  both  saliva  and  mucus.  The  resultant 
mixture  of  the  secretions  of  these  and  the  other  glands  of  the 
mucous  membrane  constitutes  what  is  ordinarily  known  as 
saliva,  though  really  it  should  be  called  mixed  saliva.  It  is  a 
transparent  watery  fluid,  and  is  somewhat  viscid  from  the 
mixture  of  mucus.  This  viscidity  allows  it  to  retain  air- 
bubbles  when  churned  by  the  action  of  the  tongue  and  checks. 
It  has  a  specific  gravity  of  about  1006  and  an  alkaline  reac- 
tion. Chemically,  it  is  mostly  (99J  per  cent.)  water,  holding 
in  solution  very  small  amounts  of  salts  and  proteids,  with  the 
addition  of  a  ferment  called  ptyalin.  The  amount  secreted 
in  twenty-four  hours  is  estimated  to  be  one  to  two  quarts  ; 
most  abundant  secretion  occurring  during  mastication. 

It  keeps  the  mouth  in  a  moist  condition,  and  so  lubricates 
the  tongue  in  speaking  and  in  chewing  ;  dissolves  the  soluble 
portions  of  the  food,  and  in  this  way  brings  them  in  contact 


NERVE-CONTROL   OF  SALIVARY  SECRETION.          93 

with  the  organs  of  taste  ;  mixes  with  the  food,  and  forms  a 
soft  and  slippery  bolus  suitable  for  swallowing.  Saliva  from 
the  front  of  the  mouth,  containing  more  water,  softens  the 
bolus,  while  the  tonsillar  and  pharyngeal  secretions,  being 
mucous,  coat  it  with  a  slippery  surface.  The  saliva  has  a 
special  digestive  function  by  the  action  of  its  ferment,  ptyalin. 

Ptyalin  :  Ptyalin  is  a  ferment  (a  non-nitrogenous  body  hav- 
ing an  uncertain  chemical  composition),  with  the  special  prop- 
erty of  converting  cooked  starch  into  maltose.  While  the  fer- 
ment itself  cannot  be  isolated  and  analyzed,  a  glycerin  solu- 
tion may  be  obtained  from  the  parotid  and  submaxillary  glands, 
which  have  been  dehydrated  by  alcohol.  This  ferment  does  not 
act  upon  any  other  body  than  starch.  The  action  of  the  ferment 
in  changing  starch  to  sugar  is  known  as  an  amylolytic  action, 
and  such  a  ferment  is  called  an  amylolytic  ferment.  The 
kind  of  sugar  resulting  from  the  action  of  ptyalin  is  maltose. 

Ptyalin  works  most  actively  at  a  temperature  of  40°  C.  and 
in  a  neutral  solution.  Its  action  is  suspended  in  an  acid  solu- 
tion, but  continues  in  a  slightly  alkaline  medium.  At  0°  C. 
its  action  is  suspended,  and  if  raised  to  65°  C.  is  destroyed. 
Most  of  the  ptyalin  (in  man)  is  found  in  the  saliva  secreted 
by  the  parotid  glands.  The  sublingual  glands  secrete  very 
little  ptyalin  (if  any),  the  submaxillary  glands  being  midway 
between  the  other  two  in  the  amount  of  ptyalin  formed. 

The  salivary  glands  do  not  become  active  until  the  subject 
is  from  four  to  six  months  old  ;  hence  the  reason  for  avoiding 
starchy  food  for  young  infants. 

Nerve-control  of  salivary  secretion :  Saliva  is  secreted  more 
abundantly  upon  the  application  of  a  stimulus.  It  is  there- 
fore increased  by  reflex  nerve-force.  The  stimuli  may  be 
mechanical  or  chemical  or  mental ;  thus  the  flow  of  saliva  is 
increased  by  taking  food  into  the  mouth  or  by  irritating  the 
inside  of  the  mouth  by  scratching  or  burning,  or  by  looking 
at  or  smelling  or  even  thinking  about  food. 

In  the  submaxillary  gland  the  chorda  tympani  nerve  is  said 
to  have  a  double  function — to  increase  the  vascularity  of  the 
gland  by  one  portion  of  its  fibres,  and  to  excite  the  secreting 
function  by  another  set  of  fibres,  the  sympathetic  nerves  of 
the  gland  acting  as  the  vaso-constrictors. 


94  DIGESTION. 

In  the  parotid  the  vasodilator  impulse  comes  also  from  the 
facial  nerve  through  the  fifth  by  the  communication  of  the 
lesser  petrosal  nerve.  The  vaso-constrictor  impulse  comes 
from  the  sympathetic. 

There  is  found  a  medullary  centre  which  controls  this  func- 
tion. 

Deglutition:  Deglutition,  or  swallowing,  is  the  process  by 
which  we  convey  food  from  the  mouth  to  the  stomach,  and 
may  be  divided  for  the  purpose  of  analysis  into  three  actions  : 
1st.  The  food  after  mastication  is  pushed  by  the  tongue 
against  the  palate,  and  so  forced  on  toward  the  fauces.  (The 
importance  of  the  tongue  should  be  remembered  by  the  sur- 
geon when  operating  on  it.  Enough  of  the  base  must  bo  left 
to  press  against  the  palate,  otherwise  deglutition  will  become 
very  difficult  or  impossible.)  2d.  As  soon  as  the  bolus  enters 
the  pharynx  it  is  pushed  on  by  the  tongue  and  by  the  con- 
traction of  the  pillars  of  the  fauces  and  the  constrictors  of 
the  pharynx  toward  the  cesophageal  opening.  The  pharyngeal 
vault  is  guarded  from  invasion  by  solid  or  liquid  food  by  the 
valve-action  of  the  soft  palate,  while  the  opening  of  the 
glottis  is  protected  by  the  simultaneous  intrinsic  muscular 
closure  of  the  rima  glottidis  and  by  the  partial  covering  of 
the  epiglottis.  When  the  muscles  of  the  fauces  and  tongue 
push  on  the  food-mass,  they  also  draw  up  the  larynx  and 
dilate  the  resophageal  opening.  3d.  The  oesophagus  grasps 
the  food,  and  a  peristaltic  wave-series  carries  it  rapidly  on  to 
the  cardiac  opening  of  the  stomach.  The  time  involved  in 
the  whole  act  of  deglutition  is  about  six  seconds.  The  be- 
ginning (1st)  of  the  act  of  swallowing  is  voluntary,  the  re- 
mainder reflex,  and  is  governed  by  centres  in  the  medulla 
oblongata  acting  through  the  cranial  nerves  which  supply 
the  parts.  The  trigeminus,  glosso-pharyngeus,  and  vagus  by 
their  sensory  and  motor  functions  act  both  in  the  capacity  of 
afferent  and  efferent  communication  with  the  medullary  centre. 

The  Stomach. 

Structure:  The  stomach  (Fig.  48)  is  an  organ  which   re- 
in   structure   the  rest  of  the  intestinal   tract;   it  is 


STRUCTURE. 
FIG.  48. 


95 


Human  alimentary  canal,  n,  oesophagus  ;  b,  stomach  ;  c,  cardiac  orifice ;  d,  pylorus  ; 
e,  small  intestine ;/,  biliary  duct;  <?,  pancreatic  duct;  h,  ascending  colon;  i, 
transverse  colon  ;  j,  descending  colon ;  k,  rectum, 


96  DIGESTION. 

hollow,  having  a  peritoneal  covering  and  a  mucous  membrane 
lining,  with  a  muscular  layer  between.  It  is  in  this  mucous 
membrane  that  the  special  function  of  the  stomach  lies,  for 
here  are  found  glands  which  secrete  the  gastric  juice.  The 
active  peristaltic  motion  churns  the  food  about  after  degluti- 
tion, and  exposes  it  thoroughly  to  the  action  of  the  digestive 
agents.  The  function  of  the  stomach  is  the  digestion  of  ]>r<>- 
teids.  When  distended  it  measures  about  fifteen  inches  from 
end  to  end,  and  about  five  inches  antero-posteriorly. 

Glands  of  the  stomach :  If  one  looks  closely  at  the  mucous 
surface  of  the  stomach,  it  is  seen  to  present  a  sort  of  reticu- 
lated (Fig.  49)  appearance,  the  meshes  being  larger  at  the 

FIG.  49. 


Free  surface  of  the  gastric  mucous  membrane,  viewed  from  above,  from  pig's 
stomach  ;  cardiac  portion ;  moderately  magnified. 

pyloric  than  at  the  cardiac  end  of  the  stomach.  It  is  in  the 
interstices  of  this  mesh  that  the  glands  open.  The  openings 
are  smaller  at  the  cardiac  than  at  the  pyloric  end,  and  the 
character  of  the  glands  changes:  we  therefore  speak  of  \\\<> 
varieties  of  gastric  glands — (1)  peptic  ;  (2)  pyloric. 

(1)  The  peptic  glands  are  arranged  in  groups  throughout 
the  stomach,  but  not  so  abundantly  at  the  pyloric  end.  They 
often  consist  of  a  simple  tube  dipping  into  the  surface  and 
lined  with  columnar  epithelium  (Fig.  50),  but  they  may  be 


GASTRIC  JUICE. 


97 


branched—^,  e.,  several    glands   may  empty  into  a  common 
duct.     The  columnar  epithe- 
lium   in    the    deeper    portion  Fro.  50. 
of  the  gland    contains  large, 
almost  globular,   cells,  which 
are  known  as  peptic  cells. 

(2)  The  pyloric  glands,  or 
mucous  glands,  like  the  peptic, 
may  be  simple  or  compound. 
The  ducts  are  larger,  and  the 
large  cells  are  wanting  (Fig. 
51).  During  digestion  the 
cells  of  both  varieties  of 
glands  become  swollen,  and 
in  them  are  found  granules 
which  are  supposed  to  be  pep- 
sin, or  that  from  which  pepsin 
is  formed. 

Gastric  juice :  When  the 
stomach  is  not  at  work  it  con- 
tains no  gastric  juice,  but  is 
bathed  in  an  alkaline  mucus. 
As  soon  as  food  enters  the 
organ,  however,  it  immediately 
begins  to  secrete  considerable 

nnantitios    nf    nn     'ir»irl     fliiirl        Compound  gastric  follicle,  from  the  car- 

1Cl>  diac  Dortion  of  the  human  stomach. 

which  soaks  into  and  mingles 
with  the  food.  The  cele- 
brated case  of  Alexis  St.  Mar- 
tin, who  had  a  gunshot-wound  resulting  in  gastric  fistula, 
enabled  Beaumont,  surgeon  U.  S.  A.,  to  investigate  accu- 
rately its  composition.  It  is  a  limpid,  colorless  fluid  of 
specific  gravity  1001—1010  and  acid  reaction.  It  contains 
about  \  per  cent,  solid  matter.  Its  composition  is  nearly — 

Water 99.50 

Pepsin .25 

Hydrochloric  acid .05 

Salts  (alkaline  chlorides  and  phosphates)  .20 

7-Phys.  100.00 


diac  portion  of  the  human  stomach. 
1,  excretory  tubes  leading  to  the  sur- 
face ;  2,  tubular  follicles  containing 
spheroidal  cells  (Kolliker). 


98 


DIGESTION. 


This  composition  is  not  constant,  as  the  proportions  vary 
considerably,  HC1,  for  example,  being  present  much  more 
abundantly  in  some  cases. 

Secretion  of  gastric  juice:  The  stomach  secretes  about 
fifteen  pints  of  gastric  juice  per  diem. 

The  hydrochloric  acid  is  probably  secreted  by  the  cubical 
parietal  cells  of  the  peptic  glands.  Very  little  seems  to  be 
formed  by  the  pyloric  glands. 

FIG.  51. 


Tubular  follicles,  from  pyloric  portion  of  pig's  stomach,  showing  their  csecal  ex- 
tremities and  epithelial  lining;  at  a  is  the  torn  end  of  a  follicle,  showing  its 
cavity  more  highly  magnified. 

The  pepsin  comes  from  the  globular  cells  in  the  peptic 
glands.  These  cells  are  supposed  to  form  a  subst:mr<- 
called  pepsinogen,  from  which  pepsin  is  derived.  Pepsin  is 
derived  for  commercial  or  for  experimental  purposes  from 
fresh  stomachs  by  scraping  the  surface  and  dissolving  out  the 
ferment  with  cold  water,  or  by  mincing  the  mucous  mem- 
brane and  extracting  the  ferment  with  glycerin  after  dehydrat- 
ing with  alcohol. 

Functions  of  the  gastric  juice :  The  principal  function  of 
the  gastric  juice  is  the  transforming  of  proteids  into  peptones. 


CHARACTERISTICS  OF  PEPTONES.  99 

This  action  depends  upon  the  presence  of  both  pepsin  and 
acid.  The  first  change  which  occurs  is  the  formation  of  acid 
albumin,  but  as  the  action  of  the  ferment  continues  the  acid 
albumin  is  transformed  to  peptone.  The  presence  of  acid  al- 
bumin is  demonstrated  by  the  addition  of  an  alkali,  which 
precipitates  it. 

The  action  of  the  pepsin  in  converting  proteids  to  peptones 
is  called  a  proteolytic  action,  and  chemically  its  action  is  to 
cause  a  hydration  of  the  proteid  molecules. 

Milk  is  curdled  in  the  stomach  by  a  ferment,  aside  from 
pepsin,  which  is  derived  from t the  gastric  juice.  This  action 
takes  place  in  the  absence  of  hydrochloric  acid.  Rennet  (de- 
rived from  the  fourth  stomach  of  calves)  is  used  for  this  pur- 
pose in  cheese  manufacture. 

Fats  are  unaffected,  except  that  the  albuminous  capsules 
of  fat-cells  in  adipose  tissues  are  digested  and  the  oil  set  free 
in  globules. 

Carbohydrates  are  unaffected. 

In  conclusion,  therefore,  it  can  be  said  that  gastric  diges- 
tion is  of  a  preparatory  character,  fitting  the  food  for  further 
digestion  in  the  intestines.  Not  only  the  carbohydrates  and 
fats  pass  the  stomach  practically  unchanged,  but  part  of  the 
proteids,  the  hemipeptones,  are  not  completely  digested. 
That  it  is  not  indispensable  is  proven  by  the  fact  that  re- 
cently the  entire  stomach  was  removed  from  a  woman,  yet 
she  showed  no  ill  effects,  but  lived  for  a  year  or  more,  and 
finally  died  from  another  cause. 

Characteristics  of  peptones:  (1)  They  are  diffusible— i.  e., 
have  the  property  of  osmosis,  or  passing  through  an  animal 
membrane.  This  is  of  great  importance  in  digestion,  for  if 
this  property  were  absent  no  animal  food  could  be  absorbed 
from  the  intestines.  (2)  They  are  very  freely  soluble  in 
water  and  neutral  solutions.  (3)  They  do  not  respond  to  the 
chemical  tests  for  other  proteid  substances.  They  are  not 
precipitated  by  heat  and  the  mineral  acids,  but  are  precipi- 
tated by  tannic  and  picric  acids  and  by  the  bichloride  of 
mercury. 

Muscular  action  of  the  stomach :  The  stomach  is  elastic, 
and  is  supplied  with  circular  and  longitudinal  muscles  in  its 


100  DIGESTION. 

middle  coat.  These  muscular  fibres  are  capable  of  producing 
peristaltic  movements  of  the  organ,  which  turn  the  food  over 
and  over  during  the  process  of  digestion.  This  elastic  pouch 
is  closed  at  each  end  by  strong,  sphincter-like,  circular  bands 
of  muscles  at  the  cardiac  and  pyloric  openings,  and  until  the 
stomach  digestion  is  well  advanced  none  of  the  contents 
escapes;  but  as  the  peptone-making  advances  the  pyloric 
opening  permits  the  escape  of  the  digested  food,  and  this  is 
aided  by  strong  peristaltic  efforts  on  the  part  of  the  stomach 
at  its  pyloric  end.  Toward  the  end  of  digestion  the  pylorus 
permits  the  escape  of  undigested  as  well  as  of  digested  mat- 
ter. The  circulation  of  the  stomach-contents  is  circumfer- 
entially  toward  the  pylorus,  but  centrally  toward  the  cardiac 
opening. 

The  digested  food  as  it  leaves  the  stomach  is  called 
chyme. 

Time  required  for  digestion :  The  time  varies  with  the  kind 
and  amount  of  food  from  one  to  five  or  six  hours.  Digestion 
is  favored  by  rest  of  the  stomach  before  eating,  by  gentle  ex- 
ercise of  the  mind  or  body,  by  an  undisturbed  mental  condi- 
tion, and  by  a  healthy  condition  of  the  body. 

Conditions  favoring  gastric  digestion :  The  temperature  of 
the  body  is  most  favorable,  and  the  presence  of  acid — prefer- 
ably HC1 — is  essential.  For  the  best  results  the  percentage 
of  HC1  should  be  about  -^th  of  1  percent.  Excess  of  acid, 
or  neutralization,  will  stop  the  process.  The  movements  of 
the  stomach  assist  digestion  by  thoroughly  mixing  the  food 
and  the  gastric  juice.  Digestive  secretion  does  not  continue 
except  during  the  presence  of  food.  Also  the  removal  of 
completed  products  assists  in  the  conversion  of  the  re- 
mainder. 

Capacity  of  the  stomach  :  About  a  quart  in  the  adult,  but 
its  muscular  walls  enable  it  to  contract  so  as  to  fit  its  con- 
tents if  much  or  little.  When  empty  the  stomach  is  tightly 
contracted. 

Nervous  mechanism  of  gastric  digestion:  The  pncumo»-as- 
trie  and  sympathetic  (splanchnic  from  the  solar  plexus)  are 
the  nerves  which  supply  the  stomach,  and  besides  then-  there 
lerous  ganglia  in  the  stomach-walls.  The  ordinary 


INTESTINAL  DIGESTION.  101 

motion-stimulus  of  the  organ  lies  in  the  intrinsic  ganglia. 
Irritation  of  the  pneumogastric  nerve  causes  contraction ;  its 
division,  cessation  of  peristalsis.  But,  further  than  this,  the 
vagus  has  control  to  a  considerable  degree  over  secretion  in 
the  stomach. 

Digestion  of  the  stomach  after  death :  When  death  occurs 
at  a  time  when  the  stomach  contains  food  and  gastric  diges- 
tion is  going  on  the  walls  of  the  stomach  are  often  partially 
digested,  even  to  such  an  extent  that  a  perforation  occurs. 
This  condition  is  often  found  in  post-mortems  on  the  human 
body.  Many  reasons  have  been  brought  forward  as  to  why 
this  does  not  occur  during  life,  but  no  entirely  satisfactory 
theory  has  yet  been  propounded.  Some  have  thought  that- 
gastric  ulcers  were  merely  an  example  of  localized  self-di- 
gestion. 

Vomiting:  The  regurgitation  of  food  from  the  stomach 
through  the  cardiac  orifice,  and  thence  through  the  mouth, 
may  occur  when  the  cardiac  opening  is  free  and  the  pylorus 
is  closed.  This  is  usually  a  reflex  act,  and  is  performed  by 
the  contraction  of  the  stomach,  aided  by  the  pressure  of  the 
abdominal  muscles  opposing  the  fixed  diaphragm.  It  may 
be  described  as  a  reversed  peristalsis.  The  stimuli  which  ex- 
cite the  reflex  may  be  either  local  in  the  stomach  or  periphe- 
ral. Violent  irritation  of  the  gastric  mucous  membrane  will 
excite  it;  also  mental  impulses,  from  ocular,  auditory,  or 
olfactory  sources;  injury  or  irritation  of  the  testis,  ovary, 
kidney,  etc.;  unusual  motion,  as  swinging  ;  certain  diseases ; 
and  effort  of  will  in  some  is  sufficient.  There  is  a  vomiting- 
centre  in  the  medulla  acting  through  the  pneumogastric 
nerve. 

Absorption  from  the  stomach:  Although  the  stomach  is  not 
designed  as  an  organ  of  absorption,  nevertheless  probably 
some  water  and  peptones  are  absorbed  by  the  capillaries  of 
the  stomach-wall. 

Small  Intestine. 

Intestinal  ( digestion :  By  the  peristaltic  action  of  the  gut 
the  food  is  carried  on  through  the  length  of  the  organ,  but  its 


102  DIGESTION. 

progress  is  more  or  less  impeded  by  the  vahruke  conniventes, 
which  are  folds  of  the  mucous  membrane  extending  trans- 
versely across  the  intestine  at  right  angles  to  its  long  axis, 
and  occupying  usually  one-third  or  one-half  of  the  circum- 
ference, but  sometimes  extending  all  the  way  around.  They 
commence  close  to  the  stomach,  and  are  well  developed  in  the 
upper  two-fifths  of  the  small  intestine.  They  then  gradually 
diminish  in  size  and  number,  and  finally  disappear  at  the 
commencement  of  the  lower  fourth.  These  folds  of  the  mu- 
cous coat  not  only  retard  the  too  rapid  advance  of  food,  but 
cause  it  to  be  thoroughly  exposed  to  the  action  of  the  diges- 
tive fluids  (Fig.  52).  Soon  after  passing  the  pylorus  food 

FIG.  52. 


Portion  of  small  intestine  laid  open  to  show  valvulse  conniventes  (Brinton). 

comes  in  contact  with  the  alkaline  secretions  of  the  small  in- 
testine and  of  the  liver  and  pancreas.  In  the  small  intestine 
the  food  is  still  further  prepared  for  absorption,  and  from  this 
part  of  the  alimentary  tract  the  digested  food  is  taken  up  for 
body-nutrition.  The  peristaltic  action  is  controlled  by  Un- 
sympathetic system  of  nerves.  Auerbach's  plexus  lies  be- 
tween the  circular  and  longitudinal  muscular  coats.  It  is 
also  known  as  the  plexus  mesentericus.  The  blood-supply  is 
also  controlled  by  the  sympathetic  system.  Meissner's plexus 
lies  beneath  the  mucous  coat,  and  is  regarded  as  the  source 
of  control  of  the  blood-supply  and  of  the  function  of  absorp- 
tion. 

Glands  of  the  small  intestine:  There  are  three  types  of 
irland-  peculiar  to  the  small  intestine:  (1)  Lieberk film's, 
(2)  Brunner's,  and  (3)  Fever's  glands. 


GLANDS  OF  THE  SMALL  INTESTINE. 


103 


FIG. 


Glands  of  Lieberkiihn :  These  glands  (or  follicles  or  crypts) 
are  thickly  distributed  over  the  whole  surface  of  the  small 
and  large  intestine,  being 
larger  in  the  large  intes- 
tine. They  are  simply  tu- 
bular depressions  in  the 
mucous  membrane,  lined 
with  columnar  epithelium, 
which  contains  occasional 
large  "  goblet  "-cells. 

Brunner's  glands  are 
found  in  the  duodenum 
alone,  and  are  situated  in 
the  submucous  tissue. 
They  resemble  the  pylo- 
ric  glands  of  the  stomach, 
and,  like  them,  are  usually 
compound  glands.  The 
duct  of  the  gland  passes  up  through  the  mucous  membrane 
and  opens  at  its  surface  (Fig.  53). 

Peyer's  glands:  These  are  of  two  varieties — (1)  solitary 
and  (2)  agminate. 

(1)  The  solitary  glands  consist  of  a  rounded  mass  of  whit- 
ish adenoid  tissue  about  ^-th  to  y^th  in.  in  diameter,  situated  in 
the  submucous  tissue,  but  often  projecting  to  the  surface  of 
the  intestine.  Each  lymphoid  mass  is  surrounded  by  Lieber- 
kuhn's  follicles  (Fig.  54). 

FIG.  54. 


A  vertical  section  of  the  dvwdenum  highly 
magnified.  1,  a  fold-like  villas;  2,  epithe- 
lium of  the  mucous  membrane ;  3,  orifices 
of  the  tubular  glands  ;  4-5,  orifice  of  a  duo- 
denal gland ;  6-7,  two  vesicles  of  the  latter, 
more  highly  magnified,  exhibiting  the  epi- 
thelial cells  lining  their  internal  surface 
(Leidy). 


Portions  of  the  mucous  membrane  from  the  ileum.  moderately  magnified,  exhibit- 
ing the  villi  on  its  free  surface,  and  between  them  the  orifices  of  the  tubular 
glands.  1,  portion  of  an  agminated  gland ;  2,  a  solitary  gland ;  3,  fibrous  tissue 
(Leidy). 


104  DIGESTION. 

(2)  The  agminate  glands  (Peyer's  patches)  consist  of 
groups  of  these  adenoid  masses,  making  "  patches  "  in  the 
mucous  membrane  \  to  3  in.  long  and  about  \  in.  wide. 

Intestinal  juice:  The  intestinal  juice,  or  succus  cuff-rim*, 
is  the  secretion  of  the  intestinal  glands.  This  secretion  is 
yellow  in  color  and  is  markedly  alkaline.  Its  effect  upon  diges- 
tion is  not  fully  understood,  but  it  probably  has  some  effect 
upon  saccharose.  However,  its  chief  function  seems  to  be  to 
supply  loss  of  fluid — L  e.,  to  take  the  place  of  that  which  is 
absorbed  as  digestion  progresses.  At  any  rate,  the  contents 
of  the  small  intestine  as  they  enter  the  colon  are  about  as 
fluid  as  when  they  leave  the  stomach. 

Other  digestive  secretions:  The  most  important  digestive 
fluids  that  act  upon  the  food  while  in  the  intestines  are  not 
derived  from  the  intestines,  but  are  poured  into  the  small  in- 
testine near  its  beginning.  These  secretions  are  two  in  num- 
ber, and  are  formed  respectively  by  the  pancreas  and  the 
liver. 

The  Pancreas. 

The  pancreas  is  an  organ  lying  in  the  upper  part  of  the 
abdomen  in  contact  with  the  duodenum  :  in  length  it  is  about 
six  inches,  and  is  thicker  at  its  right  or  duodenal  end.  It  is 
a  conglomerate  gland,  resembling  in  structure  the  salivary 
glands.  During  digestion  it  is  active,  but  is  quiescent  iu  the 
intervals.  Its  secretion,  pancreatic  fluid,  is  discharged  into 
a  main  duct  which  receives  branches  from  the  lobes  of  the 
gland,  and  is  emptied  with  the  bile  through  a  common  open- 
ing about  two  or  three  inches  beyond  the  pylorus.  During 
digestion  the  cells  of  the  organ  become  granular,  and  the 
granules  are  thought  to  consist  of  the  substance  from  which 
the  ferments  of  the  pancreas  are  derived,  -i/ntoyen,  rather  than 
of  the  ferments  themselves. 

Pancreatic  juice :  The  pancreatic  juice  is  a  clear,  colorless 
fluid,  having  an  alkaline  reaction  and  a  notably  viscid  con- 
sistency. It  coagulates  with  heat,  and  is  made  quite  gelat- 
inous by  cold.  Specific  gravity,  1015.  Its  composition 
varies. 


DIFFERENCE  IN  ACTION  OF  TRYPSIN  AND   PEPSIN.   105 

Composition  of  pancreatic  juice  : 

Water 90 

Organic  matter: 

Ferments,  ") 

Serum-albumin,    I 

Alkali-albumin,    ( 

Fats,  soaps,  etc.,J 

Inorganic  salts  (chiefly  sodium  chloride)      .    .     1 

100 

Pancreatic  ferments:  (1)  Trypsin,  a  peptone-forming  (pro- 
teolytic)  ferment,  which  continues  the  digestion  of  proteids 
begun  in  the  stomach.  It  forms  a  peptone  which  resembles 
the  stomach  peptone  in  its  reactions.  This  ferment,  unlike 
pepsin,  only  acts  in  an  alkaline  medium.  It  acts  less  vigor- 
ously upon  gelatins  and  other  nitrogenous  bodies. 

(2)  Amylopsin,  a  starch-changing  (amylolytic)  ferment,  by 
which  starch  is  converted  to  maltose,  as  by  the  ptyalin  in  the 
saliva. 

(3)  Steapsin,  a  ferment  by  which  fats  are  broken  up  from 
the  large  globules  and  emulsified  or  saponified  in  alkaline 
media.     It  is  claimed  by  some  that  this  is  not  a  ferment- 
action,  but  is  the  result  of  the  action  of  the  alkaline  intestinal 
contents  upon  the  fat. 

Of  these  processes  the  emulsifi,cation,  or  breaking  the  fat- 
globules  into  minute  particles,  is  by  far  the  more  important, 
as  it  allows  this  form  of  food  to  be  absorbed  from  the  gut. 
Milk  is  an  excellent  example  of  a  natural  emulsion. 

Sapon  i fixation  (or  soap-making)  results  from  the  fatty  acid 
combining  with  an  alkali,  forming  the  corresponding  salt  and 
glycerin — e.  g.  : 

Stearin  4-  Potassium  hydrate  =  Potassium  stearate      +  Glycerin. 


Difference  in  action  of  trypsin  and  pepsin  :  These  two  fer- 
ments act  on  proteids  in  different  ways.  Under  the  influence 
of  pepsin  the  proteid  first  swells,  then  gradually  becomes 
softer,  changes  in  color,  and  breaks  down  into  a  grumous 


106  DIGESTION. 

mass.  When  exposed  to  the  action  of  trypsin,  however,  pro- 
teids  do  not  swell  up,  but  are  eroded  or  oaten  away,  seeming 
at  times  as  though  they  were  full  of  worm-holes.  lYp.Mu 
cmi verts  proteids  iiitohemi-albumose  and  anti-albumose,  which 
it  later  converts  into  hemipeptone  and  antipeptone.  Tryp- 
sin splits  the  proteids  at  once  into  deutero-albumose,  and  alni 
carries  the  process  a  step  further  than  pepsin,  splitting  the 
hemipeptones  into  leucin  and  ty rosin. 

Function  of  pancreatic  juice  :  It  is  most  active  during  diges- 
tion, and  is  peculiar  in  having  an  effect  upon  all  forms  of  food 
which  require  preparation  for  absorption — upon  proteids, 
starches,  and  fats. 

Conditions  favoring  pancreatic  digestion :  Moderate  heat 
(100°  F.),  an  alkaline  medium,  and  the  removal  of  the  prod- 
ucts of  the  ferment-action  as  soon  as  the  change  is  com- 
pleted. 

The  Liver. 

The  liver  is  the  largest  gland  in  the  body,  and  is  situated 
in  the  upper  part  of  the  abdominal  cavity.  It  secretes  a  fluid 
known  as  the  Itilc  or  gall,  which  is  stored  in  a  bladder  lying 
attached  to  its  lower  surface.  The  functions  of  the  organ 
are  :  (1)  secretion,  (2)  excretion,  (3)  glycogenic  function,  and 
(4)  elaboration  of  urea. 

Secretion  of  the  liver:  The  secretion  of  the  liver  is  stored 
in  the  f/df/-M<i<t<1<'r  until  its  flow  is  excited  by  the  acid  dis- 
charge of  the  stomach-contents  into  the  duodenum.  It  is  an 
active  secretion,  and  not  a  passive  filtration  from  the  blood, 
for  if  a  manometer-tube  be  fastened  in  the  duct  it  will  indi- 
cate a  pressure  greater  than  that  of  the  blood.  While  the 
gall-bladder  acts  as  a  storage  reservoir,  the  bile  does  not 
-arily  enter  it,  but  may  discharge  directly  from  the 
hepatic  into  the  common  duct.  The  opening  of  the  common 
duct  into  the  duodenum  is  guarded  bv  a  sphincter-like  arrange- 
ment of  the  muscular  fibres  in  the  gut-wall.  The  gall-blad- 
der and  the  nail-duet  are  provided  with  unstriped  muscular 
fibres,  so  that  they  may  empty  themselves.  Inspiration  and 
expiration  bring  alternating  pressure  upon  the  gall-bladder, 
ami  aid  in  emptying  it. 


BILE-SALTS.  107 

Amount  of  bile :  The  quantity  varies  with  the  amount  of 
food  taken,  but  is  estimated  to  vary  between  twenty  and 
forty  ounces,  or,  approximately,  from  a  pint  to  a  quart,  in 
twenty-four  hours. 

Character  of  the  bile :  It  is  a  viscid,  almost  ropy  fluid,  of  a 
yellow  or  red  or  greenish  color  and  bitter  taste.  It  is  faintly 
alkaline  or  neutral  in  reaction,  and  has  a  specific  gravity  of 
about  1020.  Its  composition  is,  approximately  : 

Water .86 

(  Bile  salts,  9  ^ 

Organic  matter,  <  Fat  and  cholesterin,  1  V  .  13 
(  Mucus  and  pigments,  3  j 

Inorganic  salts 1 

Too 

Bile-salts :  The  bile-salts  are  sodium  glycocholate  (Fig. 
55)  and  sodium  taurocholate.  They  may  be  isolated  in  crys- 

FIG.  55. 


Sodium  glycocholate  from  ox-bile,  after  two  days'  crystallization.  At  the  lower 
part  of  the  figure  the  crystals  are  melting  into  drops,  from  the  evaporation  of 
the  ether  and  absorption  of  moisture  (Dalton). 

talline  form  from  bile,  and  are  present  in  human  bile  in  about 
equal  proportions.     They  are  soluble  and  very  deliquescent 


108 


DIGESTION. 


colorless  crystals,  which  have  the  bitter  taste  of  bile.  7Vx/ 
by  Pettenkofer's  method:  add  to  a  solution  of  bile  a  small 
amount  of  a  solution  of  cane-sugar.  On  treating  this  solu- 
tion with  pure  sulphuric  acid  drop  by  drop  there  is  first  a 
precipitation  of  a  turbid  sediment  (cholic  acid)  ;  this  is  cleared 
by  a  further  addition  of  sulphuric  acid,  and  the  solution 
a— nines  a  bright  cherry  color,  changing  to  violet,  and,  if  much 
bile  be  present,  to  deep  purple. 

Bile-pigments  :  The  bile-pigments  are  biliverdin  and  bili- 
rubin.  Both  pigments  are  found  in  human  l>ile,  but  the 
former  is  characteristic  of  the  bile  of  herbivora,  and  the  lat- 
ter, bilirubin,  of  the  bile  of  carnivora.  The  pigments  are 

FIG.  56. 


Cholesterin  from  the  contents  of  an  encysted  tumor. 

orygtallizable,  and  are  insoluble  in  water.  The  crystals  have 
the  "Teen  ;in<l  red  colors  of  the  pigments.  Qmdin's  hilc  //>•/.- 
add  fuming  nitric  (nitroso-nitric)  acid,  and  there  results  a 
play  of  colors  which  is  best  seen  when  the  bile  solution  is  in 
thin  layer  on  a  white  plate.  The  presence  of  the  bile-pig- 
ments is  shown  also  by  absorption-bands  in  the  spectrum. 
Bilirubin  is  derived  from  haemoglobin,  and  biliverdin  from 
the  bilirubin,  as  they  are  chemically  closely  allied. 


GLYCOGENIC  FUNCTION  OF  THE  LIVER.  109 

In  considering  the  death  of  the  red  blood-corpuscle,  it  has 
been  already  stated  in  the  chapter  on  the  Blood  that  the  haemo- 
globin from  the  disintegrated  red  corpuscle  is  eliminated  by 
the  liver.  This  is  the  haemoglobin  that  makes  the  bile- 
pigment. 

Cholesterin  is  a  crystallizable,  insoluble  substance  which 
belongs  to  the  alcohol  group  in  chemical  composition.  Best 
recognized  by  microscopic  appearance  of  the  crystals  (Fig. 
56),  though  it  may  be  tested  chemically  by  the  addition  of 
sulphuric  acid,  which  gives  a  red  reaction. 

Use  of  bile  in  digestion:  (1)  The  alkaline  reaction  of  the 
bile  aids  the  pancreatic  and  checks  the  pepsin  digestion ;  it 
aids  in  the  emulsion  of  the  fats,  and  is  probably  very  active 
in  this  process.  (2)  It  moistens  the  mucous  membrane  and 
favors  the  absorption  of  digested  food.  (3)  It  acts  as  a 
natural  purgative  and  as  a  natural  antiseptic,  and  in  this 
way  is  very  essential  to  the  proper  performance  of  the  diges- 
tive process.  As  a  purgative  bile  acts  by  stimulating  peri- 
stalsis. 

Excretion  of  the  liver :  The  bile  for  the  most  part,  in  nor- 
mal conditions,  is  a  sort  of  circulating  fluid  :  it  is  secreted  by 
the  liver,  poured  into  the  intestines,  and  reabsorbed  from 
them,  to  be  returned  through  the  portal  vein  to  the  liver  for 
recirculation.  There  is,  however,  a  small  proportion  of  biliary 
matter,  about  one-sixteenth,  which  is  not  absorbed,  and  this 
consists  chiefly  of  the  pigments  of  the  bile.  The  salts  are 
nearly  all  reabsorbed  in  the  assimilation.  Further  than  this, 
the  liver  is  found,  so  to  speak,  to  filter  materials  which  would 
be  poisonous  if  circulating  in  the  general  system,  and  either 
to  reject  them  at  once,  or  to  store  them  up  and  return  them 
slowly  back  to  the  intestine.  The  excrementitious  material 
from  the  liver  is  known  as  stercobilin.  Stercorin  is  found  in 
the  fa3ces,  and  is  thought  to  be  an  excretion  of  the  liver :  it 
closely  resembles  cholesterin,  and  is  supposed  to  be  a  modifi- 
cation of  cholesterin  by  digestion.  Whether  or  not  the  ster- 
corin  (cholesterin)  is  an  excretion  of  the  liver  corresponding 
to  the  urea  of  the  kidney  is  somewhat  uncertain. 

Glycogenic  function  of  *the  liver :  The  liver  normally  forms 
a  substance  resembling  starch  in  its  chemical  composition. 


110  DIGESTION. 

This  is  known  as  glycogen,  and  is  formed  from  glucose  taken 
up  by  the  portal  circulation.  Its  chemical  formula  is  that  of 
starch  (C6H10O5),  and  it  is  derived  from  glucose  (C6H12O6)  by 
dehydration,  and  is  rapidly  changed  by  diastatic  ferments  to 
glucose.  This  process  is  known  as  the  glycogenic  function 
of  the  liver :  its  use  is  the  storage  of  a  fund  of  carbohydrate 
mail-rial  (an  "animal  starch")  to  maintain  a  steady  supply  to 
the  system. 

Elaboration  of  urea :  This  subject  will  be  discussed  under 
the  Urine. 

Large  Intestine. 

Structure :  While   the  villi  and   valvulse   are   absent,  yet 
throughout  its  whole  extent  there  are  found  tubular  and  soli- 
tary glands  which  closely   resemble 
FIG.  57.  those  of   the   small   intestine.     The 

tubular  glands,  however,  are  more 
numerous,  longer,  and  more  closely 
set  together  (Fig.  57). 

Digestion :  The  chyme  which  enters 
the  large  intestine  still  continues 
under  the  influence  of  the  ferments, 
and  the  process  of  digestion  continues. 

section  of  the  mucous  mem-     The  food  ma7  "ndergo  acid  fermon- 
brane  of  the  colon,  i,  free     tation  here,  but  there  is  no  new  diges- 

surface  exhibiting  the  onh-         .  .  ~, 

ces  of  the  tubular  elands;     tive  action.     Inat  the  large  intestine 
m^Sr'88™™"^'1'     may  have  the  power  of  acting  upon 
food  is  shown  by  the  absorption  of 
fats,  proteids,  etc.,  which  are  taken  in  nutrient  enemata. 

Defecation :  The  expulsion  of  the  refuse  of  digestion  from 
the  intestine  is  partly  a  voluntary  act,  but  more  especially  re- 
flex. The  voluntary  act  is  the  pressure  of  the  abdominal 
muscles  upon  the  contained  viscera,  while  the  reflex  is  an  in- 
creased peristalsis  in  the  sigmoid  flexure  and  rectum  and  the 
relaxation  of  the  sphincter.  The  centre  which  governs  this 
act,  so  far  as  it  is  reflex,  lies  in  the  lumbar  region  of  the 
spinal  cord. 


FACTORS  FAVORING   ABSORPTION.  Ill 

ABSORPTION. 

Absorption  is  the  process  by  which  the  digested  food  is 
taken  from  the  intestines  and  carried  into  the  blood,  whence 
it  is  taken  to  nourish  the  cells.  The  same  term  is  applied  to 
the  removal  of  worn-out  material  from  the  tissues.  Chyme  is 
the  name  given  to  food  after  digestion.  By  digestion, 
the  proteids,  starches,  arid  fats,  which  were  not  dialyz- 
able,  have  become  peptones,  sugars,  and  emulsified  fat. 
All  these  products  of  digestion  are  readily  capable  of  di- 
alysis, and  therefore  ready  for  absorption.  The  absorption 
takes  place  through  the  bloodvessels  and  lymphatics  of  the 
intestine. 

By  dialysis  we  mean  the  property  of  fluids  which  enables 
them  to  pass  through  animal  membranes — osmosis.  This 
we  have  seen  is  possessed  in  a  high  degree  by  the  ingredi- 
ents of  chyle.  The  reverse  process  may  occur,  and  fluids 
(serum)  from  the  blood  may  similarly  be  drawn  into  the 
intestinal  canal,  as  is  seen  when  the  salines  are  used  as  purga- 
tives. 

Too  much  importance  must  not,  however,  be  attached  to 
osmosis  as  accounting  for  the  phenomena  of  absorption. 
Under  certain  circumstances  substances  are  absorbed  inde- 
pendently of  this  principle.  For  example,  when  tested  ex- 
perimentally outside  the  body,  sugar  is  less  diffusible  than 
sodium  sulphate,  yet  it  is  absorbed  more  rapidly  from  the 
intestine.  Certain  coloring-matters  are  not  absorbed  at 
all,  the  cells  appearing  to  exert  some  selective  action.  It 
is  also  difficult  to  explain  by  osmosis  the  absorption  of 
emulsified  fats.  It  is  probable  that  the  protoplasm  of  the 
living  cells  on  the  walls  of  the  intestine  has  some  specific 
action. 

Sites  of  absorption :  In  the  stomach  and  large  intestine 
the  absorption  is  very  much  less  than  in  the  small  intestine, 
but  there  is  reason  to  think  that  there  is  considerable  ac- 
tivity to  absorption  from  the  entire  gut  so  long  as  digestion 
continues. 

Factors  favoring  absorption:  (1)  The  valvulse  conniventes 
greatly  increase  the  area  of  the  intestinal  surface,  and  by  their 


112 


ABSORPTION. 


shelf-like  formation  delay  the  advance  of  chyme.  (2)  The 
villi  of  the  intestine  not  only  increase  the  area,  but  are  the 
special  organs  of  the  function  of  absorption.  (3)  The  con- 
traction of  the  intestine  upon  its  fluid  contents  also  favors, 
mechanically,  the  filtration  of  the  contents  through  its  walls. 
Villi  of  the  intestine:  The  villi  are  almost  innumerable, 
minute,  teat-like  projections  from  the  surface  of  the  wall  of 
the  intestine.  They  are  very  numerous  in  the  small  intestine, 
but  none  is  found  in  the  large  gut.  Each  villus  is  covered  by 

an  epithelial  layer,  and  within, 
FIG.  58.  supported  by  areolar  tissue,  is  a 

delicate  capillary  network  of 
bloodvessels,  a  muscular  layer 
(muscularis  mucosse),  and  a  more 
or  less  branched  ending  of  a  lac- 
teal vessel  (Figs.  58  and  59). 

FIG.  59. 


a 


An  intestinal  villus.  a, 
layer  of  cylindrical  epi- 
thelium, with  its  exter- 
nal transparent  striated 
portion  ;  hb.  blood  vr>sHs 
enterlngftnd  leaving  the 
villus  ;  c,  lymphatic  ves- 
sels, occupying  its  cen- 
tral axis  (Leydig). 


Patch  of  Peyer's  plands,  tVom  the  lower 
part  of  the  ileuin,  showing  villi  (mag- 
nified). 


The  ileo-Cffical  valve  slio\v>  tlie  abs<»lu1<-  alteration  which  is 
apparent  in  the  mucous  membrane  of  the  small  as  compared 
with  the  large  intestine.  On  the  side  toward  the  ileuin  are 
found  villi  in  great  numbers,  while  its  ea-cal  side  shows  none. 


DESTINATION  OF  ABSORBED  FOOD. 


113 


FIG.  60. 


The  lacteals  are  similar  to  the  lymph-capillaries   found  in 
other  parts  of  the  body. 

Changes  in  the  products  of  digestion  on  being  absorbed  :  The 
proteids  that  have  been  eaten  are  changed  by  the  digestive 
fluids,  as  already  explained,  into 
peptones.  These  peptones  are 
largely  absorbed  by  the  blood- 
capillaries  of  the  digestive  tract. 
In  passing  through  the  mucous 
membrane  of  the  intestine  the 
peptones  are  converted,  in  some 
unexplained  manner,  into  serum- 
albumin.  Hence  we  find  that  ab- 
sorbed proteids  exist  in  the  blood 
as  serum-albumin.  Unconverted 
peptones  would,  if  injected  into 
the  blood,  act  as  a  poison. 

The  carbohydrates  are  con- 
verted by  digestion  into  maltose. 
On  being  absorbed  by  the  blood- 
vessels maltose  is  converted  into 
dextrose. 

The  fats  are  highly  emulsified 
and  saponified.  They  are  ab- 
sorbed by  the  lacteals. 

Water  and  inorganic  salts  are 
absorbed  as  such  by  the  blood- 
vessels of  the  intestinal  villi. 

Peptones  and  sugars  then  are 
absorbed  by  the  blood-capillaries 
of  the  stomach  and  of  the  small 
and  large  intestines,  principally 
of  the  small  intestine.  Fats  are 
absorbed  only  by  the  lacteals,  hence  only  in  the  small  intes- 
tine ;  water  and  inorganic  salts,  principally  in  the  large  and 
small  intestines. 

Destination  of  absorbed  food :  The  food  absorbed  by  the 
lacteals  is  collected  from  all  the  lymph-spaces  in  the  villi  and 
about  the  glandular  structure  of  the  intestines,  and  is  taken 

8— Phys. 


Lacteals    and    lymphatics   during 
digestion. 


114  ABSORPTION. 

thence  into  the  larger  lacteals,  whence  it  passes  through  the 
mesenteric  lymphatic  glands  and  into  the  receptaculum  chyli 
of  the  thoracic  duct  (Fig.  60).  Hence  it  passes  on  into  the 
blood-vascular  system,  which  it  joins  at  the  root  of  the  neck 
at  the  union  of  the  left  internal  jugular  and  subclavian 
veins. 

The  food  absorbed  by  the  blood-capillaries  is  brought  to  the 
liver  by  the  portal  veins. 

On  entering  the  liver  the  portal  vein  breaks  up  into  capil- 
laries, and  thus  the  serum-albumin  and  dextrose  are  brought 
under  the  direct  influence  of  the  liver-cells. 

The  liver-cells  allow  only  a  small  part  of  the  carbohydrates 
(dextrose)  to  pass  on  and  enter  the  general  circulation.  The 
remainder  of  the  dextrose  is  acted  upon  by  a  ferment  in  the 
liver-cells,  converting  it  into  glycogen.  The  glycogen  is  then 
stored  up  in  the  liver  until  such  time  as  the  body  needs  more 
carbohydrates  than  the  food  eaten  furnishes.  When  such 
demand  is  made  upon  it  the  liver  reconverts  some  of  the 
stored-up  glycogen  into  dextrose  and  pours  it  into  the  general 
circulation. 

The  scrum-albumin  representing  the  proteid  food-stuffs 
passes  through  the  liver  and  into  the  general  circulation. 

Ultimate  use  of  absorbed  food:  The  absorbed  food  has  now 
been  followed  into  the  general  circulation.  By  the  arteries 
the  food-products  are  carried  all  over  the  body,  to  be  used  in 
building  up  the  tissues.  These  same  tissues  ultimately,  as 
the  result  of  their  lifework,  are  oxidized,  broken  up  into 
carbon  dioxide,  water,  and  other  wastes,  to  be  finally  elimi- 
nated from  the  body. 

Conditions  favoring  food-absorption  :  To  be  absorbed  by  the 
bloodvessels  or  lacteals  we  must  have  substances  in  a  Jlnid 
.v/ff/r,  and  the  more  dilute  in  solution  the  more  ready  the  ab- 
sorption ;  insoluble  substances  are  not  appreciably  affected 
by  this  process,  nor  are  any  dense  solutions  readily  taken  up. 
The  rapid  removal  of  the  absorbed  matter  and  the  rcm-iml  of 
fresh  blood  in  the  capillaries  are  of  importance.  Thus,  if 
the  portal  circulation  is  obstructed,  so  that  the  blood  is  cir- 
culated slowly  or  the  capillaries  are  tense  from  intravascular 
pressure,  absorption  will  be  slow. 


PROCESSES  OF  SECRETION  AND  EXCRETION.       115 

SECRETION. 

Secretions  are  materials  separated  from  the  blood  by  the 
cells  to  serve  some  further  purpose  in  the  animal  economy. 
These  secretions,  for  the  most  part,  consist  of  substances 
which  probably  do  not  exist  as  such  in  the  blood  itself,  but 
require  special  cells  for  their  formation  ;  for  example,  the 
liver-cells  for  the  formation  of  bile,  the  stomach-cells  for  the 
formation  of  gastric  juice,  etc.  The  mucous  and  serous 
membranes  also  act  in  this  capacity  as  well  as  the  glands. 
Examples  of  secretions  are  found  in  milk,  bile,  gastric  juice, 
tears,  etc. 

Excretions  are  materials  which  are  separated  from  the  blood 
by  cell-activity  and  discharged  from  the  body,  being  either 

FIG.  61. 


Follicles  of  Lieberkiihn,  from  small  intestine  of  dog. 

useless  or  harmful  if  retained — e.  g.,  urine,  sweat.  They  con- 
tain materials  which  exist  in  the  blood  in  the  same  form,  and 
are  merely  abstracted  from  it. 

Processes  of  secretion  and  excretion  :  Secretion  and  excretion 
are  carried  on  by  means  of  the  activity  of  the  cells  set  aside 
for  that  purpose.  In  most  cases  the  cells  are  grouped  in 
organs  which  are  known  as  glands.  The  serous  fluids  are  the 


1  hi 


SKCRKTrON 


only  notahle  exception  to  lliis  ml*-,  the  endolhelial  cells  secret 

iiiii-  without  ilic  intervention  of  complex  anatomical 

Structure  of  a  secreting  apparatus  :   The  essentials  of 
secreting  apparatus  ;irc  the  primary  or   basement  UK  inl>r<tn< ,   a 
simple  Mild  nearly  le\l  ureless  si  rue!  lire  ;   cerlain    x^/vw/  IT//X, 
ami  AAW/rxxr/x.      Those  essentials  mai    I"1  continued    in    \:iri 
oils  \v:iys,  hill  :ill  \  :irid  ics  ;ire  divided   inlo   t//,ui<lx  :ind    IIKID- 


Forms  of  secreting  glands:   (I)   SimpU  £u6utM,  or 

t/fttmls,  \vhieli  are  pits  or  depressions  in  epithelial  surface- 
lined  with  epithelial  cells.  The  mucous  surfaces  furnish  the 
BIO  i  numerous  examples  of  this  form  of  ^land,  follicles  of 
Liehcrkidm  (Kit:.  <!l).  and  Inhnlar  (mucous)  o-himU  of  ihe 
slomach  ;  hut  the  skin,  in  the  sweat  glands,  sho>\s  a  more 
Complicated  form  of  tnhnlar  inland  in  that  it  is  convoluted 
and  tortuous. 

("2)    Compound   tulmtnr    <jfttints   consist    of   a    Inhnlar   ^land 
which    suhdivides    the    main    tnhnle,    so    as    to    have     icveral 

branching  tnhules  leading  inlo 

1  1<;    62.  it.        Often       these      hranehes 

a^-ain  snhdi\  ide  so  as   to    form 
a  »TOUJ>  of  nllimale  glandular 
elements    grouped      ahoul      the 
main  tulmle,  which   acts 
duct.      This    form  of  inland    is 
found    in    kidncN  .    testlS.    -nli 
\arv    and     mammarx      j-land-. 
lirnnner's     o-lands    (  Ki^-. 
and  in  maiix   of  ihe  other  ^lan 
dnlar  structures. 

glands,  in  which  1  lie  ^landnlar 
structure  is  divi«led  inlo  lol> 
ulcs,  or  tifiin'.  These  "-hinds 
in  i\  he  regarded  as  a  relineinenl  of  the  compound  luhiilar 
VarietV,  and  example^  are  found  in  (he  sali\ar\  -dand  and  in 
the  Mi-ihoiniaii  follicles 

Processes  of  secretion :  ( 1  i  P.y  /*A//.v/V^/  procc    e       \  iz.,  Ultra 
ti"ii    and    dialysis      the    cells    are    aide    to    separate    from    the 


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din  i  MU  (ho  jwnnanonoy  uf  tht> 

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I  MX  in    Crf    &€    lun,  u,  MI  .    .iii,l,  ,  ,MIX,  i    ,  U  ,  .i-.    .1    ml,-. 

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118  SECRETION. 

so-called  trophic  influence  of  the  nervous  system,  which  di- 
rectly affects  the  secreting  power  of  a  gland  :  this  is  especially 
well  shown  in  the  case  of  the  chorda  tympani  in  its  relation 
to  the  secretion  of  the  snbniaxillary  gland. 

Correlation  of  secretions  :  There  often  seems  to  be  a  relation 
in  the  amount  of  one  secretion  to  that  of  some  of  the  others ; 
thus  in  a  diseased  condition  of  the  intestinal  mucous  mem- 
brane, with  increased  secretion,  there  will  often  be  an  in- 
crease of  the  bile  secreted,  and  perhaps  a  diminution  of 
other  secretions,  as  salivary  or  urinary.  And,  again,  unusual 
perspiration  is  followed  by  decrease  in  the  activity  of  the 
kidneys. 

Having  studied  the  general  subject  of  secretion,  the  matter 
will  be  best  pursued  if  we  study  the  individual  secreting  and 
excreting  glands. 

Serous  Secretions. 

The  serous  secretions  are  the  products  of  the  activity  of  the 
cells  of  the  pleura,  peritoneum,  pia  mater,  and  tunica  vaginalis ; 
also  of  the  synovial  membrane  of  joints,  tendon-sheaths,  etc. 
The  secretion  of  the  synovial  membranes  is  far  more  glairy 
and  viscid  than  is  that  of  the  true  serous  membrane. 

The  purpose  of  serous  secretion  is  to  lubricate  surfaces  in 
which  friction  is  undesirable.  The  serous  membranes  are 
characterized  by  having  a  single  layer  of  polygonal  endothe- 
lial  cells  covering  their  free  surface.  The  fluid  secreted  ap- 
pears to  be  identical  with  very  dilute  liquor  sanguinis  It  is 
pale  yellow  or  straw  color,  alkaline,  slightly  viscid,  and,  be- 
cause it  contains  albumin,  is  coagulable  by  heat. 


Mucous  Secretions. 

Mucus  is  secreted  by  the  mucus-cells  of  glands  opening 
onto  mucous  membrane.  It  is  a  more  or  less  viscid,  semi- 
tran-parent,  alkaline  fluid  of  high  specific  gravity,  contain- 
in-  epithelium  and  leukocytes.  It  consists  of  a  large  amount 
of  mucinj  a  little  albumin,  water,  salts,  and  traces  of  fats  and 


COMPOSITION  OF  MILK.  119 

extractives.  The  object  of  the  secreted  mucus  is  to  keep 
moist  and  soft  the  delicate  cells  of  the  mucous  membrane  ;  also 
at  the  same  time  the  mucus  acts  as  a  lubricant.  Mucous  tracts 
which  are  so  protected  are  the  digestive,  respiratory,  and 
genito-urinary. 

Mammary  Glands. 

The  mammary  glands  are  large  structures  which  are  made  up 
of  several  distinct  lobes.  Each  lobe  has  its  duct,  which  leads 
to  the  nipple,  and  there  are  about  twenty  such  lobes  and  ducts. 
The  lobes  are  subdivided,  and  the  small  lobes,  or  lobules, 
are  made  up  of  the  terminal  tubules  of  the  duct,  which  lie  in 
a  mesh  of  fibrous  areolar  tissue  containing  considerable  fat  in 
its  reticulum.  The  ultimate  divisions  (alveoli)  of  the  termi- 
nal tubules  are  lined  with  columnar  epithelial  cells,  as  are 
the  ducts  and  their  branches,  but  the  epithelium  of  the  ducts 
becomes  flat  (squamous)  near  the  nipple.  The  main  ducts 
(lactiferous  ducts)  are  sacculated,  and  during  lactation  the 
secretion  of  the  alveoli  collects  in  them,  and  is  drawn  from 
them  through  their  small  orifices  in  the  nipple.  The  flow  of 
milk  is  also  aided  by  the  presence  of  a  small  amount  of  un- 
striped  muscular  fibre  in  the  wall  of  the  ducts. 

The  mammae  are  abundantly  supplied  with  bloodvessels, 
lymphatics,  and  nerves,  and  during  pregnancy  and  lactation 
the  vessels,  as  well  as  the  gland,  undergo  considerable  increase 
in  size. 

Milk:  The  secretion  of  the  mammary  gland  is  a  bluish- 
white  fluid.  It  is  opaque,  and  this  opacity  is  caused  by  the 
presence  of  minute  fat-globules  which  are  held  suspended — 
an  emulsion.  Besides  the  fat-globules  the  microscope  shows 
in  milk  from  a  newly  active  gland  certain  albuminous  bodies 
which  are  known  as  colostrum-corpuscles.  They  are  proba- 
bly cells  from  the  gland  which  are  undergoing  fatty  degene- 
ration. Milk  is  alkaline  in  reaction,  and  has  a  specific  gravity 
of  about  1030. 

Composition  of  milk :  The  ingredients  of  milk  are  water, 
containing  in  suspension  fats  and  in  solution  casein,  serum- 
albumin,  milk-sugar,  and  salts.  Human  milk  differs  from 


120  SECRETION. 

cows'  milk  in  containing  less  proteids  and  fats  and  more 
sugar: 

Human  milk.  Cows'  milk. 

Water 890  858 

Proteids 35  68 

Fats 25  38 

Sugar 48  30 

Salts _2  _6 

1000  1000 

Cream :  The  fat-globules  rise  to  the  top  if  milk  is  allowed 
to  stand,  and  are  called  cream.  By  agitating  or  "  churning " 
the  cream  the  albuminous  envelopes  of  the  fat-globules  arc 
broken,  and  they  coalesce  to  form  a  fat  mass  known  as 
butter. 

Secretion  of  milk:  The  activity  of  the  mammary  glands 
does  not  begin  until  the  individual  has  become  pregnant — in 
fact,  the  secreting  alveoli  are  not  fully  formed  until  the  first 
pregnancy.  During  the  period  of  gestation  there  is  no  true 
milk  secreted,  but  the  cells  are  developing  and  preparing  for 
their  functions.  There  is  formed  during  the  latter  part  of 
pregnancy  a  secretion  somewhat  similar  to  milk,  called  colos- 
trum. It  differs  from  ordinary  milk  in  containing  a  larger 
quantity  of  solid  matter.  Under  the  microscope  are  to  bo  seen 
certain  granular  masses,  called  colostrum-corpuscle* ,  which  have 
been  seen  to  exhibit  contractile  movements.  Its  chief  value 
lies  in  the  fact  that  it  acts  as  a  laxative,  thus  insuring  an 
emptying  of  the  infant's  intestinal  canal.  The  formation  of 
colostrum  is  marked  during  the  first  two  or  three  days  after 
labor,  followed  by  secretion  of  true  milk. 

The  continued  secretion  of  milk  is  only  kept  up  by  the 
stimulus  of  the  nursing  infant.  If  the  child  be  weaned,  tlie 
milk-producing  cells  rapidly  cease  to  secrete.  The  nerve- 
supply  regulating  secretion  of  milk  has  not  been  definitely 
proven. 

Milk  as  a  food:  As  the  food  of  all  young  animals  it  must 
be  considered  of  the  greatest  importance;  besides  this,  as  a 
direct  food,  both  in  the  natural  state  and  in  the  derived  forms 


EPIDERMIS.  121 

of  butter  and  cheese,  it  is  one  of  the  most  used  articles  of 
adult  diet.  The  causes  which  lead  to  its  choice  in  the  dietary 
are  easily  seen  :  it  contains  all  the  elements  necessary  to  sus- 
tain life — water,  proteids,  carbohydrates,  and  fats.  As  an 
exclusive  diet  it  will  probably  sustain  life  better  than  any 
other  substance. 

Digestion  of  milk  :  When  milk  taken  as  food  enters  the 
stomach  it  is  first  acted  upon  by  rennin. 

Kennin  is  a  milk-curdling  ferment,  its  property  being  to 
convert  the  soluble  proteid  casein  into  an  insoluble  curd. 
The  digestion  of  the  curd  is  by  the  hydrochloric  acid  and 
pepsin.  The  digestion  of  the  remaining  elements  of  milk  is 
the  same  as  that  of  other  proteids,  carbohydrates,  and  fats. 

Besides  rennin  of  the  stomach,  there  are  other  milk-curd- 
ling ferments  that  will  act  upon  milk  so  as  to  cause  its  sepa- 
ration into  curds  and  whey.  They  are  found  in  the  pancreas 
and  intestine. 

"  Souring  "  of  milk :  There  is  also  a  curdling  of  milk  pro- 
duced when  an  acid  is  added  to  milk.  This  is  called  "  sour- 
ing." In  nature  the  acid  is  made  by  the  breaking  up  of 
milk-sugar  (lactose)  to  form  lactic  and  butyric  acids,  through 
the  action  of  a  micro-organism,  the  "  bacterium  lactis." 

Secretions  of  the  Skin. 

The  skin  :  The  skin  acts  as  a  general  protective  and  sensory 
covering  for  the  outer  surface  of  the  body.  It  also  acts  to  a 
certain  extent  as  an  absorbing  surface.  As  we  shall  see  later,  it- 
acts  as  an  excretory  organ  and  as  an  important  heat-regulator. 
There  are  two  layers  of  tissue  which  form  the  entire  thick- 
ness of  the  skin.  The  superficial  epithelial  layer  is  known  as 
the  epidermis  or  cuticle  ;  the  deeper  stratum,  in  which  lie  the 
active  functional  elements,  is  called  the  cutis  vera,  corium, 
or  derma. 

Epidermis  :  The  epidermis  is  a  stratification  of  epithelial 
cells,  of  varying  thickness.  The  epithelium  is  flat  and  horny 
at  the  surface  ;  in  the  deeper  portions  are  flattened  and  poly- 
hedral cells ;  and  it  is  closely  adapted  to  the  surface  of  the 
corium  beneath  it  (Fig.  63).  In  its  deeper  layer  is  found  the 


122 


SECRETION. 


FIG.  <;;-;. 


pigment  which  characterizes  the  complexion  of  individuals  and 
of  races.    Its  function  is  purely  one  of  protection.    The  growth 

to  replace  worn-out  cells  is  verv 
rapid,  and  in  cases  of  consider- 
able use  of  a  part,  with  inter- 
rupted pressure  upon  the  skin, 
the  cuticle  becomes  very  thick 
and  horny,  as  is  often  seen  upon 
the  hands  and  feet.  The  hair 
and  nails  are  modifications  of 
the  epidermal  epithelium. 

Corium  :  The  true  skin  is  a 
tough,  elastic  tissue  composed 
of  interlacing  bundles  of  con- 
nective-tissue cells  containing 
spaces  between  the  fasciculi. 
These  spaces  are  known  as 
areolce.  There  are  also  numerous 
unstriped  muscular  fibres.  This 
structure  lies  upon  a  more  or  less 
thick  layer  of  fatty  or  loose  eel  1 1 1- 
lar  tissue.  In  thecutis  are  found 
the  active  organs  of  the  skin— 
papillae,  sweat-  and  sebaceous 
glands,  and  the  hairs  (Fig.  64). 

Papillae  :  Upon  the  superficial  surface  of  the  cutis  vera 
Are  innumerable  minute  elevations  which  project  into  the 
epithelium.  They  are  very  vascular,  and  contain  the  nerve- 
endings  which  give  to  the  skin  its  sensibility,  the  sense  of 
touch.  The  papillae  are  especially  abundant  upon  the  parts 
in  which  this  sense  is  most  acute — palms,  finger-tips,  soles. 

Sweat-glands  :  Each  gland  lies  in  the  subcutaneous  fat,  and 
consists  of  a  convoluted  mass  of  tubules  which  terminates  in 
a  duct  leading  up  through  the  derma  and  epidermis,  discharg- 
ing the  secretion  of  the  gland  through  a  minute  opening. 
This  secretion  is  known  as  perxjtinifion,  or  sweat. 

Sebaceous  glands  :  The  sebaceous  glands  occur  everywhere 
over  the  entire  skin  surface  with  the  except  ion  of  the  palms 
and  soles,  and  most  abundantly  in  the  hairy  parts.  They  are 


Skin  of  the  negro,  vertical  section, 
magnified  250  diameters,  a,  a,  cuta- 
neous papilla.1;  6,  undermost  and 
dark-colored  layer  of  oblong  vertical 
epidermis-cell* ;  c,  mucous  or  Mal- 
pighian  layer;  d,  horny  layer  (K61- 
liker). 


HAIR. 


123 


intimately  connected  with  the  hair- follicles ;  and  their  ducts, 
as  a  rule,  open  into  the  follicles,  though  sometimes  they  dis- 
charge separately.  The  glands  are  aggregate  glands — that  is, 


FIG.  64. 


Epidermis 

or 
Cuticle 


Fibrous^ 
tissue  — : 


Sebaceous 
Glands 


-Glands 


Nutrient  Artery 


Sectional  view  of  the  skin,  magnified. 


are  formed  by  the  subdivision  of  the  duct  to  make  up  the 
lobules  of  the  gland.  There  is  a  delicate  plexus  of  capillary 
vessels  about  the  sacculi. 

Hair  :  A  hair  is  produced  by  a  peculiar  growth  and  modi- 


124 


SECRETION. 


FIG.  65. 
10  9 


fication  of  the  epidermis,  especially  of  the  rete  mucosum.  It 
consists  of  a  bulb  or  root  imbedded  in  the  skin  and  of  a  pro- 
jecting shaft.  It  is  composed  of  a  central  medullary  sub- 
stance, around  which  is  dis- 
posed a  thick  layer  of  elongated 
horny  cells — the  cortex.  On  the 
outside  is  a  layer  of  fine  scales, 
closely  overlapping  with  the 
edges  turned  upward,  known  as 
the  cuticle.  The  root  of  each 
hair  is  lodged  in  the  follicle,  a 
tubular  depression  of  the  skin 
descending  into  the  subcutane- 
ous fat.  At  the  bottom  of  the 
follicle  is  a  small  papilla  of  true 
skin,  by  the  projection  and  out- 
growth of  whose  cells  the  hair 
is  formed  (Fig.  65). 

Nails :  A  nail,  like  a  hair,  is 
produced  by  modified  skin.  It 
consists  of  two  layers,  a  super- 
ficial horny  one,  composed  of 
flattened  nucleated  cells  or  scales, 
and  a  deeper  soft  layer,  corre- 
sponding to  the  rete  mucosum 
of  the  epidermis.  The  back 
edge  of  the  nail — the  root — is 
received  in  the  groove  of  the 
matrix,  a  specially  modified  part 
of  the  corium.  The  growth  of 
the  nail,  like  that  of  the  hair, 
is  due  to  a  constant  production 
of  cells  from  beneath  and  behind  in  the  matrix. 

The  sweat  is  a  watery  fluid,  colorless,  slightly  turbid, 
slightly  salty  to  the  taste,  of  acid  reaction,  and  possessing  a 
peculiar  odor.  It  is  an  excrement.  Its  composition  is  some- 
what variable,  but  in  general  it  may  be  said  to  contain  about 
J  per  cent,  of  solids  suspended  and  dissolved  in  water.  These 
solids  are  fats  and  fatty  acids,  sodium  chloride,  epithelium, 


Diagram  of  structure  of  the  root  of  a 
hair  within  its  follicle.  1,  hair-pa- 
pilla ;  2,  capillary  vessel ;  3,  nerve- 
fibres  ;  4,  fibrous  wall  of  the  hair- 
follicle;  5, basement-membrane  :  6, 
soft  epidermis  lining  the  folli- 
cle ;  7,  its  elastic  cutieular  layer  ;  8, 
cuticle  of  the  hair:  9,  cortical  sub- 
stance ;  10,  medullary  substance ; 
11,  bulb  of  the  hair  composed  of 
soft  polyhedral  cells;  12, transition 
of  the  latter  into  the  cortical  sub- 
stance, medullary  substance,  and 
cuticle  of  the  hair  (Leidy). 


SECRETION  OF  SEBACEOUS  GLANDS,  125 

and  a  trace  of  urea.  Besides  these  there  is  a  considerable 
amount  of  carbonic  dioxide  (CO2)  excreted  by  the  skin. 

Nervous  mechanism  of  perspiration  :  It  is  probable  that  the 
sweat-glands  are  under  the  reflex  control  of  centres  in  the 
medulla  and  in  the  spinal  cord,  and  that  these  centres  regu- 
late this  function  of  the  skin  through  the  vaso-motor 
system. 

Amount  of  sweat :  The  amount  of  sweat  excreted  depends 
on  the  condition  of  the  atmosphere,  the  nature  and  quantity  of 
the  food,  the  amount  of  fluids  consumed,  the  exercise  taken, 
and  the  relative  activity  of  the  other  glands,  especially  of  the 
kidneys.  Certain  mental  conditions,  some  diseases,  and  drugs 
also  interfere  with  sweat- secretion.  In  general,  we  may  say 
the  amount  is  about  a  quart  in  twenty-four  'hours. 

Odor  of  sweat :  The  odor  of  sweat  varies  for  different  parts 
of  the  body,  and  markedly  for  different  races  of  mankind. 
The  odor  is  due  to  various  acids  found  in  the  sweat — formic, 
acetic,  butyric,  propionic,  caproic,  and  caprylic. 

Purpose  of  sweat :  The  sweat  is  an  excrement,  and  so  we 
consider  the  skin  as  an  excretory  organ.  The  principal  sub- 
stances excreted  in  the  sweat  are  water,  carbon  dioxide,  and 
urea. 

In  addition  to  being  a  means  of  excretion,  the  sweat  is  of 
great  value  as  a  regulator  of  body-heat.  By  evaporating  from 
the  surface  the  sweat  cools  the  body. 

Insensible  perspiration  :  When  the  secretion  of  the  sweat- 
glands  forms  in  drops  upon  the  skin  we  speak  of  this  as 
sensible  perspiration,  or  sweat.  However,  since  the  glands  are 
continuously  active,  there  are  times  when  the  fluid  evaporates 
so  rapidly  that  no  moisture  is  noticeable  upon  the  surface  ; 
this  is  called  insensible  perspiration. 

Secretion  of  sebaceous  glands :  The  secretion  of  the  seba- 
ceous glands  is  a  soft,  oily,  white  material,  and  has,  besides 
other  fats,  stearin  for  basis.  Its  use  seems  to  be  to  lubricate 
the  skin,  keeping  it  soft  and  flexible,  and  at  the  same  time,  by 
its  oily  nature,  to  prevent  maceration  of  the  skin  from  con- 
tinued exposure  to  moisture ;  and  to  check  undue  absorption 
from  the  surface.  Sebaceous  matter  is  not  excrementitious, 
but  is  a  secretion. 


126  SECRETION. 

Absorption  by  the  skin  :  In  addition  to  its  excretory  and 
secretory  properties,  the  skin  has  the  power  of  absorption. 
This  function  admits  of  the  application  to  and  absorption  by 
the  skin  of  certain  medicines,  food,  and  drink. 

In  frogs,  for  example,  the  skin  has  the  power,  if  kept 
moist,  of  absorbing  oxygen  ;  it  is  by  virtue  of  this  property 
that  a  frog  can  oxygenate  its  blood  under  water. 

Necessity  of  sweat:  Sweating  is  an  absolute  necessity  to 
life,  in  order  to  assist  the  other  excretory  organs  in  removing 
the  wastes  of  the  body.  The  symptoms  of  complete  sup- 
pression of  the  insensible  sweat  are  those  of  an  acute  poison- 
ing, together  with  pyrexia  and  exhaustion.  This  can  be 
proven  by  varnishing  the  skin  of  animals,  which  causes 
death.  A  celebrated  instance  of  this  is  the  case  of  a 
child  who,  being  covered  with  gold-leaf  to  personate  an 
angel  at  the  coronation  of  Leo  X.,  died  a  few  hours  after- 
ward. 

Kidneys  and  Urine. 

The  kidneys  are  glandular  organs  having  somewhat  the 
form  of  a  bean.  In  size  they  are  somewhat  more  than  4 
inches  in  length,  somewhat  more  than  2  inches  wide,  and 
about  1  inch  thick.  The  weight  of  each  organ  is  about  4  to  6 
ounces.  A  thin  but  rather  tough  capsule  invests  the  kidney 
(Fig.  66).  This  may  be  pulled  off  readily,  leaving  the  sur- 
face of  the  organ  smooth  and  even  and  of  a  deep-red  color. 
If  a  vertical  section  of  the  organ  be  made,  the  central  cavity 
(sinus)  will  be  noticed,  and  about  it  the  kidney-tissue.  Within 
the  sinus  are  the  apices  of  pyramidal  projections,  about  ten  in 
number  ;  and  if  the  cut  surface  be  examined  closely,  it  may 
be  noted  that  the  outer  (cortical)  portion  differs  in  appear- 
ance from  the  more  central  (medullary)  portion.  The  blood- 
supply  is  from  the  renal  artery,  and  the  nerve-supply  is  from 
the  sympathetic  system  through  the  solar  plexus.  The  kidney 
is  a  compound  tubular  gland.  The  medullary  portion  of  the 
organ  is  almost  entirely  made  up  of  tubules,  which  take 
origin  in  the  cortex  and  empty  upon  the  apices  of  the  pyra- 
mids of  Malpighi  of  the  medullary  portion  (see  below). 


URINIFEROUS  TUBULES. 


127 


FIG.  66. 


Malpighian  bodies :  In  the  cortical  portion  of  the  kidneys 
are  found  minute  tufts  of  capillaries  which  are  surrounded 

by  a  capsule  lined  with  epi- 
thelial cells  (Fig.  67) ;  and 
here  it  is  that  the  tirinifer- 
ous  tubules  arise,  the  tuft  of 
capillary  vessels  being,  as  it 
were,  built  into  the  end  of 
the  tubule. 

Uriniferous  tubules :  Be- 
ginning in  the  cortex  of  the 
kidney  at  one  of  the  bodies 
of  Malpighi,  the  minute  se- 

FIG.  67. 


Vertical  section  of  a  kidney. 


Malpighian  body. 


creting  ducts  pursue  a  tortuous  course  to  the  larger  collecting 
tubules,  which  empty  at  the  apices  of  the  pyramids  of  Mal- 
pighi into  the  calyces  of  the  kidney  (see  Ureters).  Without 
entering  minutely  upon  the  course  of  the  tubules,  it  is  impor- 
tant to  remember  that  they  form  a  loop  (of  Henle)  which 
dips  into  the  pyramid,  and  that  they  pursue  a  somewhat  tortu- 
ous course  both  before  entering  into  the  loop  of  Henle  and 
upon  returning  to  the  cortical  portion  of  the  kidney,  where 
they  empty  into  the  straight  collecting  tubules.  The  straight 
course  of  the  arms  of  Henle's  loop  and  of  the  collecting 


128 


SECRETION. 


tubules  gives  to  the  pyramids  a  finely  striated  appearance 
(Fig.  68).  These  collecting  tubules  en  masse,  together  with 
interstitial  tissue,  bloodvessels,  and  lymphatics,  make  a  "  pyra- 
mid." 


FIG. 


Diagram  of  the  tubules  ami  vascular  supply  of  the  kidney.  <>n  the  left  is  a  tubule 
alone;  in  the  middle  is  a  tubule  along  with  the  bloodvessels ;  on  the  right  an- 
bloodvessels  only.  v.  r.,  venae  rectae;  a.  r.,  arterise  rectse. 

Blood-supply  of  kidney :  On  entering  the  kidney  the  renal 
artery  bivaks  up  into  several  brandies,  which  pass  into  the 
ti— ne  proper  of  the  organ.  Branches  from  these  arteries 


URINE.  129 

(arteria  propria  renales)  have  two  determinations — (1)  into 
the  cortex  and  (2)  into  the  pyramids. 

(1)  Those  branches  (interlobular)  which  pass  into  the  cortex 
divide  to  become  the  afferent  vessels  to  the  Malpighian  bodies, 
and,  after  there  passing  through  the  capillary  tuft,  the  blood 
is  re-collected  and  goes  out  by  an  efferent  vessel.     This  effer- 
ent vessel  in  its  turn  is  broken  into  a  minute  capillary  plexus 
which  surrounds  the  uriniferous  tubules  in  the  cortex  of  the 
kidney,  and  these  capillaries  unite  to  form  the  venous  return- 
circulation  (interlobular  veins).     Thus,  this  system  has,  it  is 
to  be  noted,  two  capillary  divisions,  in  the  Malpighian  tuft, 
and  again  about  the  tubules  of  the  cortex.     There  is  also  a 
sub-capsular  capillary  division,  derived   from   certain  of  the 
interlobular  vessels  that  do  not  go  to  nor  come  from  the 
Malpighian  bodies. 

(2)  Numerous  minute  branches  (arterise  recta?)  are  given 
off,  which  pass  into  the  pyramids  as  far  as  their  apices,  and 
there  form  capillary  divisions  from  which   the  venae  recta3 
return  to  join  the  branches   from  the  cortex  and  form  the 
venaB  proprise  of  the  kidney. 

The  ureters :  Leading  from  each  kidney  to  the  bladder  is  a 
duct — the  ureter — about  the  size  of  a  goose-quill  and  from 
twelve  to  sixteen  inches  in  length.  The  ureters  are  lined 
with  mucous  membrane,  continuous  above  with  that  of  the 
pelvis  of  the  kidney,  and  below  with  that  of  the  bladder.  The 
"  pelvis  of  the  kidney  "  is  the  upper  dilated  end  of  the  ureter  ; 
and,  in  its  turn,  is  made  up  of  the  conjoined  calyces  (see 
Uriniferous  Tubules). 

The  bladder :  This,  which  forms  a  temporary  receptacle  for 
the  urine,  is  a  hollow  muscular  organ  of  a  pyriform  shape, 
lined  with  mucous  membrane,  and  situated  in  the  pelvic  por- 
tion of  the  abdominal  cavity.  The  widest  part  is  called  the 
fuiHJH*,  and  the  narrowed  part,  whence  leads  the  urethra,  is 
sometimes  known  as  the  cervix. 

Urine :  It  is  a  clear,  amber-colored  fluid  of  slightly  acid 
reaction.  It  may  develop  a  flocculent  precipitate  of  a  light 
cloud  of  mucus  upon  standing.  It  has  a  characteristic  odor 
and  a  salty-bitter  taste. 

Urine  has  a  specific  gravity  of  about  1020 ;  but  under  con- 

9— Phys. 


130  SECRETION. 

ditions  of  health  it  may  vary  from  1010  to  1030,  or  even  be- 
yond these  limits. 

( 'otwing-matter  of  urine:  The  coloring-matter  of  the  urine 
appears  to  be  identical  with  hydrobilirubin.  It  is  derived 
from  the  bilirubin  of  the  bile,  which,  being  absorbed,  passes 
out  of  the  body  in  the  urine  rather  than  in  the  faeces.  The 
varying  tints  are  probably  due  to  oxidation  of  this  sub- 
stance. 

Composition  of  urine  :  The  urine  is  an  excrementitious  fluid, 
and  may  be  considered  as  a  watery  solution  of  the  excrementi- 
tious products  of  the  retrograde  metamorphosis  of  nitrogenous 
bodies,  resulting  from  the  processes  of  life  and  action.  Chem- 
ically, it  is  a  solution  of  urea  and  urates  with  a  small  per- 
centage of  organic  salts. 

Table  of  the  Chemical  Composition  of  the  Urine. 

Water    .    .    .    • 967 

Crystallizable  nitrogenous  bodies : 

Urea 14 

Uric  acid,  free  (trace), 

Uric  acid  in  form  of  alkaline  urates, 

Hippuric  acid  and  hippurates,  !>    .         11 

Pigments,  extractives,  and  mucus, 

(All  in  small  and  constant  amounts). 

Salts: 

Inorganic — 

Chlorides  of  sodium  and  potassium, 
Sulphates  and  phosphates  of  sodium  and 

potassium, 

Phosphates  of  magnesium  and  calcium, 
Silicates  (trace), 
Organic — 
Lactates,  acetates,  and   formates,  which 

only  appear  occasionally. 
Sugar  (occasionally),  a  trace, 
Gases,  nitrogen,  and  carbonic  acid. 

1000 

Acidity  of  urine :  The  acidity  of  the  urine  is  due  to  the 


AMOUNT  OF  URINE.  131 

presence  of  acid  sodium  phosphate.  There  is  no  free  acid 
present,  as  is  shown  by  the  fact  that  no  precipitate  is  formed 
upon  the  addition  of  sodium  hyposulphite.  The  degree  of 
acidity  varies,  being  less  during  active  digestion  and  less  after 
vegetable  food.  Herbivora  have  alkaline  urine,  while  car- 
nivora  have  strongly  acid  urine  ;  but  the  herbivorous  animal 
during  fasting  has  acid  urine,  because  it  is  then  living  from 
its  own  tissues  and  is  for  the  time  a  carnivore.  After  excre- 
tion, however,  the  urine  soon  becomes  more  acid  (probably 
because  of  the  presence  of  some  fermentation),  and  at  this 
time  uric  acid  and  urates  may  precipitate.  Upon  further  ex- 
posure it  is  attacked  by  micro-organisms,  and  the  urea  is 
changed  to  ammonium  carbonate,  the  reaction  becoming  alka- 
line, and  there  is  a  precipitation  of  triple  phosphates  and 
alkaline  urates.  In  the  body  these  conditions  do  not  occur  in 
conditions  of  health. 

Secretion  of  urine  :  The  kidneys  secrete  urine  in  two  ways  : 
(1)  by  filtration  and  (2)  by  real  functional  action  of  the  epi- 
thelium. 

(1)  In  the  circulation  of  the  blood  through  the  Malpighian 
tuft  there  seems  to  be  no  active  separation  of  the  urinary  in- 
gredients by  cell-power,  but  the  water  and  saline  elements  are 
given  off  here  by  the  blood  by  a  process  of  simple  filtration. 
The  amount  of  fluid  which  passes  here  is  governed  by  the 
blood-pressure  in  the  arteries  of  the  kidney  and  by  the  fluid- 
ity of  the  blood. 

(2)  The  epithelium  of  the  uriniferous  tubules  has  secreting 
function,  and  is  able  to  separate  from  the  blood  foreign  sub- 
stances (e.  g.9  urea  or  indigo-carmine)  and  eject  them  into  the 
tubules,  and  to  manufacture  from   material  taken  from  the 
blood  new  substances  not  found  there  (e.  g.y  pigments). 

Amount  of  urine :  The  average  amount  of  urine  secreted 
daily  is  fifty-two  fluidounces,  though  as  little  as  thirty-five 
ounces,  or  as  much  as  eighty-one,  may  be  voided  within  the 
limits  of  health.  The  quantity  varies  greatly  in  health  with 
the  amount  of  fluid  taken,  of  food  consumed,  of  the  activity 
of  the  skin  evaporation,  and  somewhat  with  the  character  of 
the  food.  In  a  more  general  way  it  may  be  said  to  depend 
upon  the  condition  of  the  blood,  an  excess  of  fluids  demand- 


132  SECRETION. 

ing  increase  of  functional  activity  on  the  part  of  the  kidneys. 
In  conditions  of  disease  or  under  the  stimulus  of  drugs  the 
limits  mentioned  are  by  no  means  final,  for  in  certain  patho- 
logical conditions  the  secretion  may  be  almost  wholly  sus- 
pended or  very  greatly  increased. 

Conditions  affecting  urinary  secretion :  The  facto  is  that  favor 
the  increase  of  urine  are  those  conditions  which  favor  filtra- 
tion of  water  by  the  glomeruli  of  Malpighi — that  is,  the 
presentation  of  a  larger  amount  of  blood  to  the  action  of  these 
bodies.  This  is  accomplished— 

(1)  By  increasing  the  force  of  the  heart. 

(2)  Through  the   nervous   system   by  its  action  upon  the 
vascular,  so  as  to  produce  local  congestion.     The  effect  of  the 
nervous  system  in  increasing  the  urine  by  reflex  vaso-motor 
impulses  is  felt  most  in  the  glomeruli,  and  the  urine  is  there- 
fore very  watery. 

(3)  By  conditions  which  cause  anemia  of  other  parts,  thus 
producing  a  greater  determination  of  blood  to  the  kidneys, 
and  so  increasing  the  urinary  flow.     So  marked  is  this  that 
the  skin  and  kidneys  may  almost  be  said  to  be  complementary 
in  their  action  in  eliminating  water  from  the  system  ;  and  in 
this  regard  their  relative  activity  may  be  said  to  be  inversely 
proportional  to  one  another. 

Kirke  gives  the  following  table  (modified  from  Foster), 
which  is  useful  for  reference : 

Table  of  the  Relation  of  the  Secretion  of  Urine  to  Arterial 

Pressure  (Kirke). 
A.  Secretion  of  urine  may  be  increased — 

a.  Ry  increasing  the  general  blood-pressure — by 

1.  Increase  of  the  force  or  frequency  of  the  heart-beat. 

2.  Constriction  of  the  small  arteries  of  areas  other  than 

that  of  the  kidney. 

b.  By  increasing  the  local  blood-pressure  by  relaxation  <>f  flu' 

renal  artery,  without  compensating  relaxation   <  /*<  - 
where — by 

1.  Division  of  the  renal  nerves  (causing  polyuria). 

2.  Division  of  the  renal  nerves  and  stimulation  of  the 

cord  below  the  medulla  (causing  greater  polyuria). 


MICTURITION.  133 

3.  Division  of  the  splanchnic  nerves ;  but  the  polyuria 

produced  is  less  than  in  1  or  2,  as  these  nerves  are 
distributed  to  a  wider  area,  and  the  dilatation  of 
the  renal  artery  is  accompanied  by  dilatation  of 
other  vessels,  and  therefore  with  a  somewhat  di- 
minished general  blood-supply. 

4.  Puncture  of  the  floor  of  the  fourth  ventricle  or  me- 

chanical irritation  of  the  superior  cervical  ganglion 
of  the  sympathetic,  possibly  from   the  production 
of  dilatation  of  the  renal  arteries. 
B.  Secretion  of  urine  may  be  diminished — 

ft.   By  diminishing  the  general  blood-pressure — by 

1.  Diminution  of  the  force  or  frequency  of  the  heart- 

beats. 

2.  Dilatation  of  capillary  areas  other  than  that  of  the 

kidney. 

3.  Division  of  the  spinal  cord  below  the  medulla,  which 

causes  dilatation  of  the  general  abdominal  area,  and 
urine  generally  ceases  being  secreted. 

b.  By  increasing  the  blood-pressure — by  stimulation  of  the 

spinal  cord  below  the  medulla,  the  constriction  of 
the  renal  artery  which  follows  not  being  compen- 
sated for  by  the  increase  of  the  general  blood- 
pressure. 

c.  By  constriction  of  the  renal  artery — by  stimulating  the 

renal  or  splanchnic  nerves  or  the  spinal  cord. 

Course  of  the  urine  :  The  urine  collected  in  the  tubules  of 
the  kidney  passes  into  the  pelvis  of  the  kidney,  and  is  carried 
to  the  urinary  bladder  in  irregular  quantities  by  the  ureter. 
The  ureters  simply  act  as  ducts,  and  do  not  store  up  urine, 
nor  do  they  usually  actively  eject  it  into  the  bladder.  As  a 
few  drops  of  urine  collect  in  the  pelvis  of  the  kidney,  they 
run  into  the  bladder,  the  action  of  the  two  kidneys  not  being 
in  alternation  nor  absolutely  regular  in  point  of  time.  Re- 
gurgitation  from  the  bladder  is  prevented  by  the  oblique 
course  of  the  ureter  through  the  muscular  wall  of  the  blad- 
der. 

Micturition  :  When  the  bladder  is  filled  the  act  of  emptying 


134 


SECRETION. 


it  is  called  micturition.  It  is  a  voluntary  act,  aided  by  the 
involuntary  reflex  contraction  of  the  muscular  coat  of  the 
oriran  itself.  The  voluntary  muscles  involved  are  those  of 
respiration — the  diaphragm  and  the  abdominal  muscles.  So 
far  as  micturition  is  involuntary,  it  is  a  reflex  depending  upon 
a  centre  in  the  lumbar  spinal  cord. 

Urea  is  a  chemical  body,  the  formula  being  CH4N2O  (Fig. 
69).     The  nitrogen  atom  is  derived  from  the  "combustion. 

FIG.  69. 


Urea,  prepared  from  urine,  and  crystallized  by  slow  evaporation  (Lehmann). 

of  proteid  material.  Hence  we  infer  that  the  amount  of  urea 
excreted  gives  us  an  index  of  the  amount  of  proteid  material 
consumed  by  the  body.  The  used-up  nitrogenous  matters  of 
the  body  may  be  derived  from  :  (1)  the  food  (urea  being 
greatly  increased  by  a  nitrogenous  meal) ;  (2)  the  metabolism 
of  the  tissues. 

The  result  of  the  "  combustion  "  of  nitrogenous  material  is 
not  at  once  found  in  the  blood,  but  exists  as  some  antecedent 
of  urea  (probably  carbonate  of  ammonium)  until  the  blood 
reaches  the  liver.  Under  the  action  of  the  liver-cells  the  an- 
tecedent of  urea  is  converted  into  urea.  The  urea  thus  formed 
remains  in  the  circulation  until  the  blood  reaches  the  kidney  ; 
here  the  urea  is  excreted.  Thus  it  is  seen  that  the  kidncv- 


VASCULAR  GLANDS.  135 

cells  play  no  part  in  the  formation  of  urea,  but  merely  exert 
a  selective  action  upon  it  for  excretory  purposes. 

Amount  of  urea  excreted  :  The  amount  varies,  but  it  may  be 
considered  to  be  about  one-half  the  solid  constituents  of  the 
urine.  Roughly  speaking,  the  urinary  solids  may  be  regarded 
as  4  per  cent,  of  the  total,  and  the  urea  (including  the  uric 
acid  and  urates)  about  1.5  to  5  per  cent.  This  proportion  is 
very  variable,  and  there  may  be  urea  in  healthy  urine  to 
exceed  2J  per  cent.,  or  in  a  much  less  ratio  than  5  per 
cent. 

Method  of  estimating  solids  :  A  useful  rule  for  approxi- 
mately estimating  the  total  solids  in  any  given  specimen  of 
healthy  urine  is  to  multiply  the  last  two  figures  representing 
the  specific  gravity  by  2.33.  Thus,  in  urine  of  specific  grav- 
ity 1025,  25' X  2.33  =  58.25  gr.  of  solids  in  1000  gr.  of  urine. 
In  using  this  method  it  must  be  remembered  that  the  limits 
of  error  are  much  wider  in  diseased  than  in  healthy  urine. 

Urea  as  a  waste  :  Urea  is  capable  of  still  further  oxidation, 
and  so  would  be  a  source  of  further  chemical  potential  energy  ; 
but  urea  is  excreted  before  it  is  fully  oxidized,  and  so  is  a  real 
waste. 

Uric  acid :  Of  the  other  constituents  of  urine,  uric  acid 
is  the  most  important,  it  being  one  of  the  forms  in  which 
nitrogen  is  eliminated.  It  usually  exists  in  the  urine  in  the 
form  of  urate  of  ammonium  or  sodium.  It  probably  comes, 
like  urea,  from  food-disintegration.  Some  consider  it  to  be 
an  imperfectly  oxidized  form  of  urea.  The  amount  found  in 
the  blood  is  especially  increased  in  gout. 

Hippuric  acid  :  This  is  one  of  the  few  important  constitu- 
ents of  urine  which  is  produced  in  the  kidneys  themselves, 
being  formed  from  benzoic  and  amido-acetic  acids.  It  is  also 
formed  in  the  liver.  It  is  another  form  of  nitrogenous  elim- 
ination, but  may  come  from  tissue-waste  as  well  as  food-dis- 
integration. It  exists  in  slightly  larger  quantity  than  does 
uric  acid. 

Vascular  Glands. 

The  vascular  glands,  or  ductless  glands,  are  a  collection  of 
glandular  structures  that  possess  no  ducts  and  apparently  do 


136 


NUTRITION. 


not  seem  to  be  associated  in  either  secretion  or  excretion. 
Ductless  glands  include  the  spleen,  thyroid,  thymus,  and 
tonsils. 

Purpose  of  ductless  glands  :  No  definite  function  has  l><<n 
asi-ribed  to  the  ductless  glands  ;  but  we  do  know  that  the  ex- 
tirpation of  certain  of  these  structures  is  attended  with 
serious  results  to  the  subjects.  For  example,  congenital  de- 
fects of  the  thyroid  produce  the  condition  known  as  cretin- 
ism. 

Table  of  Secretions. 


Secretion  : 

Secreting  organ  : 

Reaction  : 

Main  Purpose  : 

Sebum; 

Sebaceous   glands    of 

Acid; 

To  oil  the  skin. 

the  skin  ; 

Mucus; 

Mucous   cells  of  mu- 

Alkaline ; 

Lubricant  and  diluent. 

cous  membranes  ; 

Serous  secretion; 

Serous  membranes  ; 

Alkaline; 

Lubricant  and  diluent. 

Tears; 
Saliva; 

Lachrymal  glands  ; 
Salivary  glands; 

Alkaline; 
Alkaline; 

To  moisten  conjunctive. 
To  moisten    food  mid  di- 

(inatrir juice; 
f<iicni.<<  nit  riciis; 

Stomach; 
Intestines; 

Acid; 
Alkaline; 

gest  carbohydrates. 
To  digest  proteids. 
To  dilute  the  divine. 

1'niKicatic  juice: 

Pancreas  ; 

Alkaline  ; 

To   digest   proteids,  fats. 

and  carbohydrates. 

Bile; 

Liver; 

Alkaline;        Part  of  the  bile  is  used  in 

digestion      and      reab- 

sorbed.    Part    is  a  true 

excretion     ;  bile-pig- 

ments). 

Milk; 

Mammary  glands  ; 

Alkaline; 

Food. 

Sweat  ; 

Sweat-glands  of  skin  ; 

Acid; 

Elimination  of  water,  car- 

bon dioxide,  and   urea. 

Regulates  body-temper- 

ature. 

Urine; 

Kidneys; 

Acid; 

Elimination  of  water  and 

urea. 

NUTRITION. 

By  nutrition  we  mean  the  physiological  principles  which 
preserve  the  normal  conditions  of  the  structure  and  function 
of  the  body,  so  far  as  refers  to  the  balance  between  the  in- 
come and  out<ro  of  material.  While  it  is  almost  an  impos.-i- 
bility  to  study  this  subject  exactly,  yet  an  idea  of  the  modes  of 
expense  and  income  may  he  gained  by  consideration  of  data 
which  are  fairly  well  settled.  In  considering  the  income  and 
expenditure  of  the  body  it  is  always  necessary  to  bear  in  mind 
thai  all  the  factors  are  variable  and  the  results  inconstant,  for 
the  income  often  exceeds  the  expense,  and  viceversti,  in  life. 


RESULTS   OF  BODY-EXPENDITURE.  137 

Sources  of  income  to  the  body  :  Food  and  drink  and  oxygen 
are  the  factors  of  the  income,  and  may  be  calculated  about  as 
follows  for  twenty-four  hours  : 

Food  (chemically  dry) 16  ounces. 

Water  (as  drink  and  as  combined  with  solid 

food) 80      " 

Oxygen  (absorbed  by  lungs) 26       " 

Total,  122  ounces. 

Expenditures  of  the  body :  The  more  important  are  those 
by  the  ordinary  excretory  channels — lungs,  skin,  kidneys,  and 
intestines. 

From  the  lungs  there  are  exhaled  every  twenty-four  hours — 

Of  carbonic  acid,  about     ...  30  ounces. 

Of  water 10       "        40  ounces. 

Traces  of  organic  matter. 
From  the  skin — 

Water 23       " 

Solid  and  gaseous  matter  ...     1  ounce.    24       " 
From  the  kidneys — 

Water 50  ounces. 

Organic  matter 1-J.     " 

Minerals  and  salines Jounce.  52       " 

From  the  intestines — 

Water 4  ounces. 

Various    organic  and    mineral 

substances 2       "          6       " 

Total,  122  ounces. 

Thus  we  may  represent  the  schematic  plan  of  income  and 
expense  as  about  equal  ;  but  it  must  be  borne  in  mind  that 
the  plan  only  represents  an  average  result  of  both. 

Variation*  in  the  rate  of  income  and  expenditures  are 
shown  by  changes  in  the  body- weight. 

Results  of  body-expenditure :  In  return  for  the  amount  of 
food,  drink,  and  oxygen  the  body  has  consumed,  we  have  to 
show  for  it : 


138  NUTRITION. 

(1)  The  growth  of  the  body  and  secretion  of  its  necessary 
materials,  as  well  as  the  maintenance  of  the  tissues,  subjected 
as  they  are  to  the  wear  incident  to  the  continuance  of  life 
and  function. 

(2)  The  continuance  of  physical  conditions  suitable  to  life 
in  the  form  of  heat  and  motion.     The  actual  combustion  of 
carbon  (/.  e.,  oxidation)  must  be  sufficient  to  maintain  the  ani- 
mal heat  and  the  nourishment  of  the  muscles  upon  which  the 
continuance  of  life  depend. 

(3)  Net-roil*  energy,  as  in  the  regulation  of  all  physiologi- 
cal processes  by  the  reflexes,  as  well  as  in  voluntary  mental 
and  nervous  action. 

Energy  of  the  body :  The  daily  work  of  the  body  has  been 
calculated  to  be  about  3400  foot-tons.  Of  this  about  one- 
tenth  has  been  considered  to  be  exhausted  in  involuntary 
muscular  action  (circulation,  respiration,  etc.)  and  in  volun- 
tary motion,  while  the  remainder  (nine-tenths)  is  expended 
in  maintaining  the  body-heat.  Another  method  of  consider- 
ing this  enormous  force  may  be  of  use :  it  is  equivalent  in 
heat  to  that  required  to  raise  nearly  fifty  pounds  of  water 
from  the  freezing-  to  the  boiling-point ;  or  in  mechanical  force 
it  is  sufficient  to  raise  the  body  of  a  man  weighing  one  hun- 
dred and  fifty  pounds  to  a  height  of  eight  and  one-half  miles. 

Effect  of  starvation :  There  is  a  loss  of  weight  in  all  the 
tissues,  but  it  is  in  the  loss  of  the  fat  that  the  change  is  most 
marked  :  the  fat  almost  entirely  (93  per  cent.)  disappears  after 
death  from  starvation.  The  sense  of  hunger  gives  way  to  a 
sense  of  pain  ;  thirst  is  excessive  ;  sleep  is  absent ;  progressive 
weakness  accompanies  increasing  emaciation  ;  the  exhalations 
of  the  skin  and  lungs  are  foetid;  and  diarrhoea  with  convul- 
sions or  delirium  often  precedes  death.  Death  occurs  with 
absolute  deprivation  of  both  food  and  drink  at  the  end  of 
about  a  week  (six  to  ten  days),  though  life  may  be  considera- 
bly prolonged  by  small  quantities  of  food  or  water.  The 
temperature  of  the  body  falls  before  death  very  considerably 
(30°  C.),  and  it  has  been  considered  that  death  results  from 
cold,  no  fuel  being  furnished  to  maintain  animal  heat.  The 
body  decays  rapidly  after  death  from  starvation. 

"  Exclusive  "  diet :  The   result  of   feeding  animals  exclu- 


NITROGENOUS  EQUILIBRIUM.  139 

sively  on  a  single  article  of  diet  (sugar,  gum,  oil,  etc.)  is 
practically  the  same  as  that  of  starvation,  except  that  death 
does  not  occur  until  the  end  of  four  or  five  weeks.  In  man 
the  exclusive  diet  of  isolated  communities  often  results  in  the 
breaking  down  of  tissue  and  general  malnutrition. 

Effect  of  over-feeding:  An  excess  of  nitrogenous  food,  if 
digested,  increases  the  metabolic  work  of  the  glanular  organs 
(especially  of  liver  and  kidneys),  and  induces  disease  in  those 
organs  and  faulty  excretion  of  nitrogenous  matter.  This 
may  be  obviated  or  delayed  by  active  physical  exercise.  Car- 
bohydrate food  in  excess  is  stored  up  in  the  form  of  fat, 
which  may  be  excessive,  with  resulting  fatty  infiltration  of 
the  viscera,  or  it  may  show  as  glycosuria. 

An  excess  of  any  food  is  apt  to  pass  undigested  through  the 
intestines  and  undergo  putrefactive  changes,  with  resulting 
gaseous  distention  :  the  carbohydrates  are  especially  apt  to 
give  rise  to  this  disturbance. 

Normal  diet :  There  should  be  a  general  diet  of  well-cooked 
food,  and  it  should  contain  about  the  amount  of  carbon  and 
nitrogen  which  is  excreted  ;  that  is,  it  should  maintain  an 
equilibrium.  This  is,  commonly,  about  two  pounds  of  solid 
food  and  two  quarts  of  fluid.  The  proportion  of  the  various 
kinds  of  food  varies  considerably,  but  in  a  general  way  for  a 
healthy  man,  one  may  divide  the  solid  food  somewhat  in  this 
way :  nitrogenous  food  (meat),  about  -|  pound ;  hydrocarbon 
and  fat-food  (bread,  vegetables,  and  butter),  about  1^  pounds. 
Besides  this,  the  food  will  contain  from  1  to  2  ounces  of  salts 
and  a  varying  amount  of  sugar. 

"  Nitrogenous  equilibrium  " :  When  an  animal  is  fed  exclu- 
sively upon  a  nitrogenous  diet,  it  is  found  that  after  a  time 
the  egested  nitrogen  approaches  and  finally  balances  that 
taken  in  as  food.  This  is  known  as  the  "  nitrogenous  equilib- 
rium." But  at  the  same  time  the  animal  may  increase  in 
weight,  and  this  occurs  by  the  formation  of  fat  which  is 
stored  up  in  the  tissues.  The  nitrogenous  equilibrium  is 
more  easily  maintained  by  the  addition  of  carbohydrates  to 
the  food. 

It  is  also  known  that  the  fat  of  the  body  not  only  comes 
from  the  fat  we  eat,  but  is  also  made  from  carbohydrates  and 


140  ANIMAL  HEAT. 

proteids.  So,  too,  carbohydrates  may  be  manufactured  from 
proteids.  Hence  the  animal  fed  on  nitrogenous  diet  exclu- 
sively may  store  up  some  fat  that  has  been  manufactured  in 
its  body  from  the  proteids. 

Assimilation :  It  seems  almost  needless  in  closing  the  sub- 
ject of  nutrition,  to  remind  the  student  that  the  body  derives 
no  benefit  from  the  food  ingested  unless  the  food  is  asMini- 
lated. 

To  be  assimilated  the  food  must  be  properly  digested,  then 
properly  absorbed  by  the  blood  and  lymph,  and  finally  become 
part  of  the  body-tissues.  Then,  too,  to  be  a  source  of  chemi- 
cal potential  energy,  the  absorbed  food  must  be  capable  of 
further  oxidation. 

ANIMAL  HEAT. 

The  normal  temperature  of  the  body  is  about  98.5°  F.  (37° 
C.).  This  temperature  is  not  invariable,  but  in  the  superfi- 
cial cavities,  mouth,  and  axilla,  which  are  convenient  for  as- 
certaining the  body-temperature,  this  is  nearly  exact.  In  the 
internal  organs  the  thermometer  may  indicate  as  high  as  100° 
F.  in  normal  conditions.  In  the  rectum  the  temperature  is 
about  1  °  F.  higher  than  in  the  mouth  or  armpit.  In  health  the 
temperature  is  maintained  constantly  with  but  slight  varia- 
tions, due  to  marked  changes  in  surrounding  air  temperature, 
age,  exercise,  sex,  etc.  The  temperature  in  health  varies  to 
the  extent  of  1°  to  1.5°  F.,  according  to  the  time  of  day  or 
night,  being  lowest  late  at  night  or  in  the  early  morn  ing, 
while  it  is  highest  late  in  the  afternoon.  This  correspond-  to 
the  usual  temperature-ranges  in  fever,  when  the  minimum  is 
in  the  early  morning,  the  maximum  in  the  late  afternoon. 

Sources  of  heat:  (1)  Principally  from  the  oxidation  of  the 
tissues  during  katabolism  of  the  body-structure.  The  tissues 
of  the  body,  as  has  been  previously  mentioned,  are  derived 
fn»m  the  organic  food-stuffs.  Hence  we  owe  our  main  supply 
of  body-heat  to  the  oxygen  of  the  air  and  the  organic  food- 
stuffs. 

(2)  Chemical  action  going  on  during  digestion  of  food  is 
also  productive  of  some  heat. 


REGULATION  OF  HEAT.  141 

(3)  Friction  of  muscles  upon  one  another,  friction  of  blood 
in  capillaries,  and  all  forms  of  friction,  are  productive  of  a 
little  heat. 

(4)  Warm  media  about  the  body,  warm  drinks  and  foods. 
Of  these  various  sources  only  the  oxidizing  of  body-tissue 

generates  enough  heat  to  keep  the  body-temperature  up  to  the 
standard.  The  main  seat  of  this  oxidizing  is  in  the  muscles, 
which  form  so  large  a  part  of  the  organism.  Therefore,  we 
can  say  that  the  principal  part  of  the  total  heat  produced 
within  the  body  is  generated  by  muscular  activity.  Active 
exercise  may  raise  the  body-temperature  from  1°  to  2°  F. 

Loss  of  heat:  (1)  Blood  circulating  at  the  surface  of  the 
body  is  cooled  by  the  colder  air.  Although  in  ordinary  health 
the  external  application  of  cold,  as  by  baths,  has  only  a  slight 
effect  on  the  temperature,  it  is  otherwise  in  the  case  of  high 
fever.  In  these  cases  a  tepid  bath  may  reduce  the  tempera- 
ture several  degrees,  the  effect  lasting  in  some  cases  for  many 
hours.  This  method  of  reducing  high  temperature  is  success- 
fully applied  in  cases  of  sunstroke  and  certain  fevers,  espe- 
cially typhoid. 

(2)  The  evaporation  of  sweat  dissipates  a  vast  amount  of 
heat. 

(3)  Loss  of  heat  is  considerable  by  the  lungs,  though   less 
than  that  from  the  skin  :  the  air  is  warmer,  in  usual  condi- 
tions, after  leaving  the  lungs  than  before  it  has  entered  them. 

(4)  Warming  the  excretions  of  the  body  (faBces,  sweat,  and 
urine)  is  another  factor  in  loss  of  heat. 

Regulation  of  heat :  The  amount  of  heat  generated  can  be 
regulated  by  diminishing  the  source  or  increasing  the  elimina- 
tion of  heat,  and  vice  versd.  The  loss  of  heat  is  principally 
regulated  by : 

(1)  The  amount  of  blood  sent  to  the  surface  to  be  cooled  ; 
this  is  regulated  by  the  vaso-motor  nerves;  (2)  the  in- 
crease or  decrease  in  sweat  secretions.  The  supply  of  heat 
depends  on  the  activity  of  tissue-metabolism,  resulting  from 
exercise,  mental  activity,  etc. 

Diseases,  such  as  fevers,  that  are  accompanied  by  a  rise  of 
temperature,  owe  that  rise  to  either  a  marked  increase  in 
katabolism  or  diminished  elimination  power,  or  to  both. 


142 


MUSCLE. 


Centres  for  heat-regulation  :  There  are  reasons  for  believing 
that  there  are  nerve-centres  exciting  the  heat-production  in  the 
tissues  (thermogenic  centres),  and   centres  which  check   the 
metabolism  of  tissue,  and  thus  control  the  temperature  (in- 
hibitory heat-centres).     This  is  not  entirely  proven,  nor  are 
these  centres  exactly  localized.     We  do  know  that  the  inner- 
vation  of  a  part  is  necessary  for  the  main- 
FIG.  70.  tenance  of  its  warmth,  aside  from    vaso- 

motor  causes  for  alteration  of  temperature. 
Limits  of  body-temperature  :  In  ordinary 
pathological  conditions  the  temperature 
does  not  remain  long  at  a  point  below 
95°  F.  nor  above  105°  F.  without  fatal 
results.  Under  extreme  conditions  of  pro- 
longed exposure  to  cold  and  the  algid  stage 
of  cholera,  recovery  has  occurred  after  a 
bodily  temperature  as  low  as  75°  F.  On 
the  other  hand,  in  some  cases  of  extreme 
fever,  as  from  sunstroke,  recovery  has  been 
noted  after  a  temperature  of  110°-112°  F. 


MUSCLE. 

Varieties :  Muscle-tissue  consists  of 
three  distinct  types:  1.  Nou-xtr'uttnl,  or 
plain  muscle-fibre.  This  is  "  involuntary/7 
or  not  under  the  control  of  the  will. 

2.  Striated  muscle,  which  is   under   the 
control  of  the  will,  or  "voluntary." 

3.  Striated  muscle,   but    not    under   the 
control  of  the  will,  hence  "  inrn/Htifttri/" 

Examples  of  the  first  class  are  the  mus- 
cles of  the  intestines,  walls  of  the  arteries, 
etc.     The  skeletal   muscles  make  up  the  second  class.     The 
heart-muscle  is  the  only  example  of  the  third  class. 

Microscopic  appearances :  Ao/*-.s7/vV/AW  /////xrA-//.vxm  is  made 
Op  df  bundles  of  elongated,  spindle-shaped  cells.  Kadi  cell  has 
an  oblong  nucleus  and  is  flattened  (Fig.  70).  In  length  they 
are  about  ^J-^th  to  ^th  inch,  and  about  ^Vu^1  "K'n  'n 


Nnn-st  rinted  element- 
ary fibres,  from  the 
human  colon,  a, 
treated  with  ^acetic 
acid,  showing  the 
corpuscle's ;  l>,  frag- 
ment of  a  detached 
fibre  not  touched 
with  acid. 


MICROSCOPIC  APPEARANCES. 


143 


width.  The  cells  are  bound  into  bundles  by  an  albuminous 
cement,  and  these  again  into  larger  bundles  by  areolar  tissue. 
Striated  voluntary  muscle-tissue  consists  of  bundles  of  long 
muscle-cells  or  fibres.  Each  fibre  is  completely  enveloped  in 
a  sheath,  the  sarcolemma,  and  the  whole  bundle  of  fibres  is 
bound  together  by  a  delicate  connective-tissue  framework. 

FIG.  71. 


A,  portion  of  a  medium-sized  human  muscular  fibre  (magnified  nearly  800  diame- 
ters). B,  separated  bundles  of  fibrils,  equally  magnified:  a,  a,  larger,  and  b,  b, 
smaller  collections ;  c,  still  smaller ;  d,  d,  the  smallest  which  could  be  detached. 

A  number  of  these  fasciculi  are  joined  together  to  make  up 
the  gross  anatomical  muscle.  On  examining  the  muscle-fibre 
itself,  it  will  be  seen  to  consist  of  alternate  segments  of  light 
and  dark  matter,  giving  the  fibre  a  striped  appearance  (Fig. 

These  fibres  are  about  an  inch  in  length  and  ^poth  inch  in 
diameter.     They  join  the  connective-tissue  cells  of  a  tendon 


144 


MUSCLE. 


FIG.  72. 


or  aponenrosis  or  another  muscle-fibre  by  adhesion  of  the 
sarcolerama  at  the  ends,  and  thus  unite  the  muscle-bundles 
in  a  firm  mass ;  and  this  union  is  further  strengthened  by  the 
cohesion  of  the  fibres. 

The  st nation  of  the  heart-muscle  fibres  is  not  so  marked  as 
in  ordinary  muscle,  and  the  form  of  the  fibres  is  different, 
for  they  are  branched  and  more  slender.  Each  fibre  is  nucle- 
ated, a  large  oval  nucleus  occurring  at  the  centre.  The  appear- 
ance of  the  heart-fibres  indicates  that  they  occupy  an  internu- 
diate  position  between  typical  plain  and  striped  fibres  (Fig.72). 

Muscle — general  properties  :  (<t) 
Un  striated  muscle-tissue  acts 
slowly,  is  not  under  the  control 
of  the  will,  acts  continuously  for 
quite  long  periods  of  time,  and 
is  slowly  exhausted. 

(6)  Involuntary  striated  muscle 
(heart)  acts  quickly,  is  not  under 
control  of  the  will,  acts  for  a 
short  period,  and  recuperates 
rapidly.  Under  this  condition 
of  rapidly  alternating  periods  of 
activity  and  repose,  the  heart- 
muscle  does  its  work  throughout 
the  life  of  the  individual. 

(c)  Voluntary  striated  MH *<•/<• 
(skeletal)  acts  rapidly,  is  under 
control  of  the  will,  and  recuper- 
ates quickly  (but  not  so  rapidly 
as  heart-muscle). 
Chemistry  of  muscle:  About  75  per  cent,  of  muscle-tissue 
is  water.  Proteids  make  up  about  15  per  cent.  Of  these, 
the  chief  constituent  is  myosinogen,  which  appears  t<>  bear 
the  snne  relation  to  living  muscle  as  fibrinogen  does  to  blood. 
It'  1>\  cold  \ve  delay  the  coagulation  of  muscles  removed  from 
animals  immediately  after  death,  we  can  express  a  viscid  fluid 
of  slightlv  alkaline  reaction,  known  as  muscle-plasma.  This 
muM'le-plasma,  when  exposed  to  ordinary  temperatures,  coag- 
ulates much  in  the  same  way  as  docs  blood-plasma,  inyosin 


Muscular  fibres  of  the  heart  (Quain) 


PHYSIOLOGY  OF  MUSCLE.  145 

being  formed.  In  a  short  time  the  clot  will  contract  and 
squeeze  out  a  fluid  resembling  blood-serum.  Myosin  differs 
from  fibrin  in  many  of  its  reactions.  It  belongs  to  the  glob 
ulin  class  of  proteids.  Fat,  glyeogen,  organic  and  inorganic 
salts  (chiefly  potassium)  make  up  the  remaining  10  per  cent. 
The  fat  exists  as  minute  strips  between  the  fasciculi.  The 
glyeogen  is  stored  up  to  serve  as  a  supply  of  chemical  poten- 
tial energy.  The  amount  of  glyeogen  present  in  resting  mus- 
cle is  about  -J-  per  cent. 

Physiology  of  muscle  :  Muscle  may  exist  in  three  different 
conditions :  those  of  rest,  activity,  and  rigor. 

Muscle-rest:  During  rest  a  muscle  has  a  slight  but  very 
perfect  elasticity.  It  can  be  stretched  to  a  considerable  ex- 
tent, but  always  returns  at  once  to  its  former  condition.  In 
the  living  body  the  muscles  are  always  in  a  condition  of  sligkt 
tension,  which  gives  mechanical  advantages.  Even  during  a 
state  of  rest  the  muscle  takes  oxygen  from  the  blood  and 
gives  up  carbon  dioxide  to  it.  The  reaction  of  a  resting 
muscle  is  neutral  or  faintly  alkaline. 

Muscle  during  activity :  The  peculiar  property  of  muscle- 
fibre  is  its  contractility,  which  is  excited  by  all  kinds  of  stim- 
uli direct  and  indirect.  This  property  is  soon  lost,  unless  the 
supply  of  arterial  blood  is  kept  up.  Muscles,  especially  the 
striated,  possess  a  certain  kind  of  sensibility  due  to  the  sen- 
sory nerve-fibres  which  end  in  them.  They  are  but  slightly 
sensible  to  pain,  the  sensations  produced  being  rather  those 
of  the  condition  of  the  muscle,  as  to  fatigue,  cramp,  etc.;  or 
else  of  muscular  sense,  as  to  position  of  the  muscles,  com- 
parison of  weights,  etc. 

After  activity  the  reaction  is  acid,  due  to  the  development 
of  sarcolactic  acid  or  lactates  by  the  breaking  up  of  the  gly- 
eogen in  the  muscle.  There  is  also  an  increase  in  water  and 
carbon  dioxide. 

Only  a  little  proteid  material  is  oxidized  during  muscular 
activity.  This  is  shown  by  the  fact  that  after  severe  exercise 
the  amount  of  urea  excreted,  although  increased  somewhat, 
is  not  increased  commensurately  with  what  would  have  been 
the  case  had  the  proteid  furnished  the  chemical  potential 
energy. 

10— Phys. 


146 


MUSCLE 


Actions  of  muscles  as  levers  :  Most  of  the  voluntary  mus- 
cles in  the  body  may  be  regarded  as  sources  of  power  for 
moving  the  bones  viewed  as  levers.  All  levers  are  divided 
into  three  classes,  according  to  the  relative  position  of  the 
power,  the  weight  to  be  moved,  and  the  axis  of  motion  or 
fulcrum.  The  different  movements  of  the  foot  offer  an  illus- 
tration of  all  three  kinds  of  levers  :  The  first  kind  (Fig.  73), 

FIG.  73. 


i  ii  in 

Illustration  of  levers  of  all  three  orders  (Huxley). 
W,  weight  of  resistance  ;  F,  fulcrum  ;  P,  power. 

where  the  fulcrum,  F,  is  between  the  source  of  power,  P,  and 
the  weight  or  resistance,  ,W,  is  illustrated  when  the  foot  is 
raised  and  the  toe  tapped  upon  the  ground,  the  ankle-joint 
being  the  fulcrum.  The  second  kind  of  lever,  where  W  is 
between  F  and  P,  is  illustrated  when  the  body  is  raised  upon 
the  toes,  the  ground  being  the  fulcrum.  The  third  kind  of 
lever,  where  P  is  between  F  and  W,  is  illustrated  when  a 
weight  is  held  up  by  the  toes,  the  ankle  being  the  fulcrum 
and  the  anterior  group  of  muscles  on  the  leg  the  source  of 
power.  The  forearm  also  acts  as  a  lever  of  this  sort  when 
a  weight  is  lifted  in  the  hand. 

Oxygen-supply  :  Muscle  receives  its  oxidizing  agent — oxy- 
gen— from  the  blood  coursing  through  the  vessels  contained 
in  the  muscle.  Even  during  repose  the  muscle  takes  up 
oxygen  from  the  blood  and  gives  back  carbon  dioxide.  The 
muscle  also  stores  up  within  itself  a  certain  amount  of  oxy- 
gen, which  can  be  called  upon  to  do  work  even  if  the  blood- 
supply  be  stopped.  To  prove  this  it  is  only  necessary  to  cut 
a  muscle  out  of  the  body  and  cause  it  to  contract  in  a  cham- 
ber of  nitrogen.  As  a  result  of  these  contractions  the  muscle 


LATENT  PERIOD.  147 

throws  off  a  quantity  of  CO2  as  a  product  of  oxidation.  The 
oxygen  necessary  for  this  oxidation  comes  from  the  supply 
stored  up  in  the  muscle  as  the  only  source,  there  being  no 
blood-supply  and  the  atmosphere  of  the  chamber  in  which 
the  experiment  is  conducted  consisting  only  of  nitrogen. 

During  muscular  activity  a  greater  supply  of  oxygen  is 
needed,  and  this  is  supplied  by  a  dilatation  of  the  bloodves- 
sels of  the  part.  Systematic  exercise  of  a  muscle  educates 
the  arterioles  supplying  that  muscle  to  remain  in  a  condition 
of  dilatation.  This  increase  in  the  blood-supply  not  only 
provides  an  increase  of  oxygen  during  activity,  but  during 
repose  carries  an  increased  amount  of  nourishment  to  the 
muscle,  with  the  result  that  the  muscle  increases  in  size  and 
power.  Hence  the  value  of  "  training." 

Muscle-fatigue  :  After  performing  its  function  of  contraction 
for  a  certain  length  of  time  the  muscle  is  less  active  in  its 
response  to  stimuli,  and  finally,  in  spite  of  the  strongest  im- 
pulses, fails  altogether  to  act.  This  is  "  fatigue  "  of  a  muscle, 
a  phenomenon  with  which  we  are  all  familiar.  After  a  suit- 
able rest  the  muscle  recuperates  and  is  as  active  as  ever. 

The  reason  for  this  fatigue  is  that  during  the  muscle's 
activity  a  number  of  effete  poisonous  products,  the  result  of 
the  active  katabolism,  have  been  formed  more  rapidly  than 
the  power  of  removal  by  the  outgoing  blood.  After  a  time 
the  accumulation  of  poison  is  so  great  as  to  paralyze  the  mus- 
cle, so  that  no  further  activity  takes  place  until  the  excess 
has  been  removed. 

The  first  effect  of  fatigue  is  seen  in  the  increased  latent 
period  and  decrease  in  the  strength  of  the  contraction. 

Muscle — latent  period  :  By  latent  period  is  meant  the  time 
that  elapses  after  a  stimulus  has  been  applied  to  a  muscle  and 
before  the  muscle  acts. 

We  speak  of  the  "  apparent "  latent  period  and  the 
"true"  latent  period. 

By  "  apparent "  latent  period  is  meant  not  only  the  time 
consumed  by  the  impulse  in  awakening  the  muscle  into 
activity,  but  also  the  time  consumed  by  the  impulse  in  reach- 
ing the  muscle  (say  in  travelling  along  the  nerve). 

"  True  "  latent  period  is  the  actual  time  consumed  between 


148 


MUSCLE. 


the  arrival  of  the  impulse  at  the  muscle  and  the  beginning 

contraction.     The  time  lor 

FIG.  74.  the   true   latent   period    is 

about  one    one-hundredth 
of  a  second. 

Contractility  :  The  im- 
portant use  of  this  power 
is  to  do  "  work  " — /.  e.,  the 
conversion  of  the  potential 
chemical  energy  of  the 
muscle  into  heat  and  visi- 
ble motion. 

If  one  watches  a  muscle 
contract,  he  will  see  that 
the  muscle  becomes  much 
thicker  and  shorter;  but 
the  volume  does  not 
change.  The  fact  that 
there  is  no  chaiiyc  of 
volume  during  contraction 
may  be  proved  by  placing 
a  muscle  in  a  vessel  filled 
with  fluid  to  a  given  mark. 
The  muscle  is  now  made 
to  contract,  and  it  is  noted 
that  the  level  of  the  fluid 
remains  unchanged. 

Owing  to  the  increased 
metabolism  during  func- 
tional activity,  there  is 
heat  liberated,  hence  an 
increase  of  temperature. 

Path  of  stimulus  for  con- 
traction :  In  the  living 
body  the  impulse  causing  contraction  of  a  muscle  arises  in  the 
centres  of  brain  or  spinal  cord,  and  travels  thence  by 
means  of  anterior  nerve-roots  and  the  somatic  nerves  going  to 
the  particular  muscle  (Fig.  74).  The  nerve  that  supplies 
a  given  mii-cle  as  it  enters  that  muscle  breaks  up  into  a  num- 


representation  of  cerebral 
and  spinal  motor  cells  with  axons.  1, 
cerebral  cell ;  2,  axon  ;  3,  4,  collaterals ;  4', 
end-tufts;  5,  spinal  cells;  6,  axon;  7, 
limit  of  spinal  cord  ;  A7.  motor-nerve;  S, 
muscle ;  9,  muscle  end-plate  (Kauber). 


CONTRACTILITY  OF  MUSCLE. 


149 


her  of  branches  that  are  distributed  to  all  parts  of  the  mus- 
cle. The  terminal  ends  of  the  nerve-fibres  are  small  cellular 
elements  called  nerve  end-plates  or  end-organs  (Fig.  75).  As 
a  rule,  these  end-organs  are  scattered  in  great  numbers 
throughout  the  muscle.  By  means  of  these  end-plates  the 
impulse  from  the  nerve  is  transmitted  to  the  muscle-fibres. 
Contractility  an  inherent  property  of  muscle  :  Although 
under  ordinary  circumstances  an  impulse  to  contract  is  sent  to 
a  muscle  through  the  intervention  of  its  nerve  and  end-plates, 
nevertheless  the  impulse  may  be  administered  directly  to  the 
muscle  itself  and  the  result  be  a  contraction. 

FIG.  75. 


Nerve-ending  in  muscular  fibre  of  a  lizard  (lacerta  viridis).  a,  end-plate  seen  edge- 
ways ;  b,  from  the  surface  ;  s,  s,  sarcolemma ;  p,  p,  expansion  of  the  axis-cylinder. 
In  b  the  expansion  of  the  axis-cylinder  appears  as  a  clear  network  branching 
from  the  divisions  of  the  medullated  fibre.  Highly  magnified  (Kuhne). 

To  prove  that  a  stimulus  may  be  administered  directly  to 
muscle-fibre  with  a  resulting  contraction  the  following  exper- 
iment will  be  described  : 

Liberate  the  sciatic  nerve  from  the  surrounding  tissues  in 
the  thigh  (say  the  right)  of  a  frog ;  but  do  not  destroy  the 
connection  of  this  exposed  nerve  with  the  gastrocnemius  mus- 
cle or  the  spinal  cord.  Pass  a  ligature  about  the  right  thigh 
so  as  to  include  all  the  tissues  except  the  sciatic  nerve.  Tie 
the  ligature  tightly.  The  purpose  of  this  ligature  is  to  shut 


150  MUSCLE. 

off  all  blood-supply  to  the  lower  part  of  the  limb.  Xow 
poison  the  frog  with  curare.  Curare  is  the  Indian  arrow- 
poison,  and  kills  by  paralyzing  the  end-plates  in  all  the  mus- 
cles. In  the  frog  experimented  upon,  the  poison  is  carried  to 
all  parts  of  the  body  except  to  the  right  leg  below  the  liga- 
ture. The  frog  lies  as  though  completely  paralyzed. 

Now,  with  an  electrical  battery  stimulate  the  right  sciatic 
nerve  ;  the  right  gastrocnemius  contracts.  Stimulate  the  left 
sciatic  ;  no  result.  During  the  stimulation  of  both  the  right 
and  the  left  sciatics  the  nerves  showed  that  they  were  carry- 
ing impulses  (proven  by  a  galvanometer) ;  hence  the  lack 
of  activity  in  the  left  leg  is  due  to  the  curare  having  affected 
either  the  muscle  itself  or  the  end-organs.  On  the  right  side 
the  blood  carrying  the  curare  has  been  prevented  (by  the  lig- 
ature) from  reaching  the  muscle  or  its  end-plates. 

Now  apply  the  electrical  stimulus  directly  to  each  gastroc- 
nemius in  turn ;  both  will  be  found  to  contract  and  with 
equal  vigor. 

This  experiment  proves  the  following  facts :  (1)  Curare 
paralyzes  a  muscle  by  inhibiting  the  end-plates  of  the  nerves  ; 
hence"  (2)  the  nerve-endings  in  the  left  gastrocnemius  being 
paralyzed,  the  stimulus  that  made  the  left  gastrocnemius  con- 
tract necessarily  exerted  its  influence  on  the  muscle  direct,  and 
not  by  the  intervention  of  the  end-plates. 

Another  proof  may  be  offered  to  the  same  end,  as  follows : 
the  gracilis  muscle  in  the  frog  is  practically  free  from  nerve 
end-organs  in  its  lower  part,  and  yet  the  lower  part  of  the 
muscle  contracts  as  readily  to  direct  stimulation  as  does  any 
other  muscle.  An  additional  proof  is  that  the  heart  of  the  em- 
bryo begins  to  beat  some  time  before  the  nerve  end-organ* 
have  developed  within  the  heart-muscle. 

Artificial  stimuli:  A  muscle  may  be  stimulated  to  activity 
either  by  irritating  the  muscle  itself,  or  by  sending  impulses 
to  the  muscle  through  the  intervention  of  its  motor  nerve. 

The  stimuli  employed  are :  (1)  chemical,  (2)  mechanical, 
(3)  thermal,  (4)  electrical.  The  last  (electrical)  is  the  most 
practical  and  most  frequently  used. 

To  study  the  effects  of  muscular  contraction  a  myograph  is 
necessary.  A  myograph  consist  of  a  drum  or  cylinder  cov- 


EFFECT  OF  GALVANIC  SHOCK.  151 

ered  with  smoked  paper.  The  drum  is  made  to  revolve  by 
clockwork  at  a  definite  rate.  The  nerve-muscle  preparation 
is  so  arranged  that  when  the  muscle  contracts  a  lever  is  made 
to  trace  a  curve  on  the  smoked  paper.  This  curve  is  called 
a  myogram,  and  by  studying  the  curve  one  can  learn  the 
amount  and  character  of  the  contraction. 

Galvanic,  faradic,  and  interrupted  currents  :  A  galvanic  cur- 
rent is  a  continuous  flow  of  electricity  directly  from  the  bat- 
tery. 

A  faradic  current  consists  of  a  direct  current  passing 
through  a  coil  of  wire ;  about  this  coil  is  wrapped  a  second 
coil,  carefully  insulated  from  the  first  coil.  The  current  pass- 
ing through  the  primary  coil,  induces  a  current  in  the  second- 
ary coil.  It  is  the  secondary  current  that  is  applied  to  the 
nerve  to  be  experimented  upon. 

An  interrupted  or  alternating  current  is  a  faradic  current  in 
which  the  primary  current  is  rapidly  made  and  broken  by  an 
automatic  interrupter. 

Response  to  stimuli :  It  has  been  found  that  striped  and 
unstriped  muscles  react  to  stimuli  in  a  somewhat  different 
manner.  This  difference  is  probably  due,  for  the  most  part, 
to  their  differing  structure,  but  may  possibly  be  due  in  some 
degree  to  their  differing  modes  of  connection  with  the  nervous 
system.  When  a  stimulus  is  applied  to  a  striped  voluntary 
muscle  there  is  an  instantaneous  contraction  of  the  part  irri- 
tated, and  of  that  only.  This  contraction  ceases  the  moment 
the  stimulus  is  withdrawn.  If,  on  the  other  hand,  any  part 
having  involuntary  muscle — for  instance,  the  bladder  or  in- 
testines— is  stimulated,  the  contraction  comes  on  more  slowly, 
extends  beyond  the  part  stimulated,  and  continues  for  some 
time,  with  alternating  relaxation,  after  the  stimulus  is  with- 
drawn. 

Effect  of  galvanic  shock  :  The  instantaneous  application  and 
removal  of  a  galvanic  shock  to  a  nerve-muscle  preparation 
result  in  a  single  twitch  of  the  muscle.  Although  it  is  stated 
above  that  the  application  is  "  instantaneous,"  it  is  shown  by 
experiment  that  the  impulse  is  not  appreciated  by  the  nerve 
unless  the  flow  of  current  lasts  at  least  0.0015  of  a  second. 
On  examining  the  curve  traced  by  the  muscle  on  the  myo- 


152 


MUSCLE. 


graph,  there  are  noted :  (a)  the  latent  period — i.  e.,  the  time 
elapsed  after  the  application  of  the  current  before  the  con- 


Base-line. 


Diagram  of  muscle-curve,    a,  point  of  application  of  current ;  b,  point  of  beginning 
contraction  ;  c,  maximum  ;  d,  return  to  normal. 

traction  commenced  ;  (b)  a  gradual  rise  in  the  curve  until  the 
maximum  is  reached,  and  then  a  gradual  curve  down  to  the 
base-line  (Fig.  76). 

Fio.  77. 


Opening  shock. 


The  time  a-b  is  the  latent  period,  and  in  the  case  of  a  frog's 
•rust  rocnemius  is  about  y^th  of  a  second.  The  total  curve  in 
the  same  muscle  lasts  about  -t^th  of  a  second. 

If,  instead  of  applying  and  removing  the  galvanic  current 
in  close  succession,  the  current  be  allowed  to  flow  for  some 


INTERRUPTED  CURRENT.  153 

time  through  the  nerve-muscle  preparation,  two  contractions 
and  relaxations  are  noted.  One  contraction  and  relaxation 
takes  place  when  the  current  is  applied,  but  during  the  rest 
of  the  flow  of  the  current  the  muscle  remains  in  a  state  of 
repose.  The  second  contraction  and  relaxation  occurs  when 
the  current  is  broken.  The ' contraction  at  the  "make"  of 
current  is  greater  than  that  at  the  "  break  "  (Figs.  77  and  78). 

From  the  fact  that  the  muscle  remains  quiescent  during  the 
flow  of  the  current  after  the  first  shock,  the  theory  is  deduced 
that  it  is  not  the  change  in 

state,    but  the  rapidity  of  FIG.  78. 

the  change  in  state,  which 
irritates  the  muscle  into  con- 
traction. This  is  proven 
by  the  fact  that  a  large 
amount  of  electrical  cur- 
rent can  be  poured  into  a 
nerve-muscle  preparation 
without  exciting  a  contrac-  closing  shock, 

tion,  provided   the  current 

be  gradually  applied  and  very  slowly  increased.  On  the  other 
hand,  a  small  amount  of  electricity  if  rapidly  administered 
will  produce  a  sharp  contraction. 

Induced  current :  A  single  shock  from  an  induced  current 
produces  the  same  result  as  that  of  a  galvanic  current  of  in- 
stantaneous duration. 

A  prolonged  application  of  the  induced  current  produces  the 
contraction  on  the  "  make  "  and  a  contraction  on  the  "  break  " 
similar  to  that  of  the  galvanic  current,  except  that  the  "  break  " 
contraction  is  greater  than  the  "  make  "  contraction. 

Interrupted  current:  The  interrupted  current,  consisting 
as  it  does  of  rapidly  alternating  "  makes "  and  "  breaks," 
produces  a  series  of  rapidly  succeeding  shocks  on  the  nerve- 
muscle  preparation.  The  result  is  that  the  muscle,  after  the 
period  of  contraction  is  over,  has  no  time  to  relax  before  a 
second  shock  is  received,  which  tends  to  a  fresh  contraction. 
Hence  the  muscle  remains  in  a  state  of  continuous  contraction 
until  the  stimulus  is  removed  or  the  muscle  wears  out.  This 
condition  of  continuous  contraction  is  called  tetanus  (Fig.  79). 


154 


MUSCLE. 


7 


Muscle — electrical  state :  By  a  rise  in  electrical  state  is 
meant  an  increase  in  the  height  of  the  curve  in  succeeding 
contractions,  on  the  application  of  single  shocks.  It  is  as 

though  the  muscle  became  more 
FIG.  79.  sensitive  and  more  responsive  to 

the  second  shock  than  to  the  first, 
and  more  so  to  the  third  than  to 
the  second,  etc.  This  rise  in  elec- 
trical state  is  observed  for  the 
first  six  to  ten  shocks.  It  is  as 
though  the  muscle  "limbered 
up  "  in  the  first  few  shocks  by  a 
little  preliminary  exercise  until  it 
reached  its  power  of  doing  its  best. 
Currents  of  rest :  When  a  living 
curve  of  tetanus.  muscle  is  tested  by  means  of  the 

galvanometer  after  removal  from 

the  body,  it  is  found  to  develop  certain  electrical  currents 
known  as  muscle-currents  or  currents  of  rest.  They  are 
strongest  from  the  centre  of  the  muscle  toward  the  cut  end, 
though  certain  minor  currents  are  developed  with  the  elec- 
trodes in  closer  proximity.  The  cut  ends  of  a  muscle  are 
always  electro-negative  to  its  equator.  This  phenomenon 
cannot  be  observed  in  uninjured  muscle  when  in  the  bodv, 
but  any  injury  will  render  the  injured  portion  electro-nega- 
tive to  the  rest  of  the  muscle.  This  condition  ceases  with 
the  power  of  contraction,  and  cannot  be  demonstrated  in  dead 
muscle. 

When  the  muscle  is  made  to  contract,  the  galvanometer- 
needle,  which  has  indicated  the  passage  of  an  electri- 
cal current  during  rest,  flies  quickly  back  toward  the  /ero, 
indicating  the  cessation  of  the  current  of  rest.  This 
action  is  known  as  the  negative  variation  of  the  galvanom- 
eter, and  as  soon  as  the  contraction  of  the  muscle  has  ceased 
the  instrument  again  indicates  the  presence  of  the  current 
of  rest. 

The  causes  are  not  yet  fully  determined,  but  these  cur- 
rents are  probably  due  to  chemical  changes  resulting  from 
physiological  degeneration.  It  has  been  held  that  such 


PFLUGER'S  LAW  OF  CONTRACTION.  155 

currents  occur  naturally  in  muscle  as  the  result  of  certain  of 
the  cells  exciting  electro-motive  forces,  but  the  former  theory 
seems  the  more  plausible. 

Excitability  and  conductivity  :  These  terms,  although  similar 
as  to  the  results,  really  mean  very  different  things. 

Excitability,  or  irritability,  refers  to  the  activity  of  response 
a  nerve  may  show  to  a  given  electrical  shock  ;  whereas  conduc- 
tivity means  the  power  of  one  part  of  a  nerve  to  conduct  an 
impulse  generated  at  another  part  of  the  nerve. 

A  moderate  current  while  passing  through  a  nerve  pro- 
duces no  shock,  but  the  excitability  of  the  nerve  at  the  point 
where  the  kathode  is  placed  is  increased  (this  increase  at  the 
kathodic  area  is  called  katelectrotonus) ;  at  the  same  time  the 
excitability  of  the  anodic  area  is  lessened  (anelectrotonus). 
On  removing  the  current  the  excitability  at  the  kathodic  area 
falls,  and  the  excitability  at  the  anodic  area  rises. 

Ou  the  other  hand,  during  the  flow  of  a  moderate  current 
there  is  a  marked  diminution  in  the  conductivity  of  the  nerve 
at  the  kathodic  area,  even  to  the  extent  of  rendering  the 
kathodic  area  impervious  to  conduction,  without  seriously 
affecting  the  anodic  area.  On  removing  the  moderately  strong 
current  the  nerve  instantly  returns  to  its  normal  conductivity. 
If  very  strong  currents  be  used,  conduction  is  completely  lost 
at  both  the  anodic  area  and  the  kathodic  area  during  the  flow 
of  the  current ;  and  when  the  current  is  removed  the  nerve 
does  not  at  once  return  to  a  normal  state  of  conductivity,  but 
remains  impaired  for  a  little  while. 

Pfluger's  law  of  contraction  :  It  has  already  been  shown  that 
the  stimulation  of  a  nerve-muscle  preparation  by  a  galvanic 
current  will  result  in  a  contraction  only  at  the  "make"  and 
at  the  "  break "  of  the  current ;  this  is  true  only  if  the 
current  be  of  medium  strength,  regardless  of  whether  the 
current  be  " ascending"  or  "descending."  But  the  results 
are  different  if  the  current  be  very  weak  or  very  strong. 

The  following  table,  known  as  Pfluger's  table,  shows  the 
effects  at  a  glance  : 


156 


MUSCLE. 


Current-strength. 

Ascending  current. 

Descending  current. 

"Make." 

"Break." 

"  Make." 

"Break." 

Weak  current  .... 
Medium  current    .   . 
Strong  current   .   .   . 

Contraction. 
Contraction. 

Contraction. 
Contraction. 
Contraction. 

Contraction. 

Contraction. 
Contraction. 

Ascending  and  descending  currents :  By  an  ascending  cur- 
rent we  mean  a  position  of  the  electrodes  such  that  the  elec- 
trical flow  is  from  the  periphery  (muscle)  to  the  centre  (brain) 
—i.  e.j  the  anode  or  positive  pole  is  nearer  the  muscle  and  the 
kathode  or  negative  pole  is  nearer  the  nerve-cell.  The  de- 
scending current  is  the  reverse  and  the  poles  are  transposed. 

The  explanation  of  the  results  is  simple,  if  we  hear  in  mind 
the' effects  on  the  nerve  of  the  various  strengths  of  currents. 

A  galvanic  current  is  stronger  on  the  "  make  "  than  on  the 
"  break."  Hence  if  we  reduce  the  strength  of  our  current 
so  that  the  "  break "  shock  is  so  weak  as  to  fail  to  give 
any  result,  our  "  make/7  being  somewhat  stronger,  would  still 
influence  the  muscle  so  as  to  cause  a  contraction.  This,  too, 
would  be  regardless  of  the  direction  of  the  current.  This 
explains  the  first  part  of  the  "  law,"  namely,  that  regarding 
weak  currents. 

In  explaining  the  second  part  of  the  law,  it  is  necessary  to 
bear  in  mind  that  the  nerve-vibrations  start  from  the  region 
of  the  kathode  on  closing  the  current;  but  on  opening  tin- 
current  the  nerve-vibrations  start  at  the  anodic  area;  also  to 
bear  in  mind  that  moderate  currents  diminish  the  conductivity 
at  the  kathodic  area  without  affecting  the  anodic  region,  anil 
on  removing  the  current  the  nerve  at  once  returns  to  normal. 

So  we  find  on  closing  a  descending  current  of  moderate 
strength,  the  excitation  starting  at  the  kathode  can  readily 
pass  to  the  muscle  and  produce  a  contraction.  On  opening 
the  current,  the  excitation  starts  at  the  anode  and  readily 
travels  along  the  nerve  past  the  kathodic  area  (which,  on 
opening  the  current,  returned  to  normal  conductivity),  and 
so  on  to  the  muscle. 

If  we  take  an  ascending  current,  on  closing,  the  impulse 


NERVE-MUSCLE  PREPARATION.  157 

goes  from  the  kathode  down  the  nerve,  past  the  unaffected 
anodic  area,  to  the  muscle.  On  opening  the  current,  the  im- 
pulse passes  from,  the  anode  directly  to  the  muscle. 

For  the  third  part  of  the  law  we  must  remember  that  very 
strong  currents  reduce  conductivity  at  both  anode  and  kathode, 
and  on  removing  the  current  the  loss  of  conductivity  does  not 
at  once  disappear.  So,  to  study  it  in  detail,  let  us  assume 
a  strong  ascending  current.  On  making  the  current  we  re- 
move the  conductivity  of  the  anodic  area,  and  the  impulse 
starting  at  the  kathode  cannot  travel  by  the  impervious  anodic 
area,  and  hence  no  contraction  results.  On  opening  the  current 
the  impulse  from  the  anode  passes  to  the  muscle  and  a  contrac- 
tion follows.  With  a  descending  current,  we  find  on  closing 
that  the  impulse  starting  from  the  kathode  travels  to  the  mus- 
cle unhindered  and  a  contraction  results ;  but  on  opening  the 
current  the  impulse  starting  at  the  anode  travels  along  the 
nerve  until  it  reaches  the  area  where  the  kathode  was.  This 
area  the  impulse  cannot  pass  (for  the  conductivity  does  not 
return  for  some  time)  and  no  contraction  results. 

Position  in  the  body:  During  repose  a  muscle  is  not  in  a 
state  of  complete  relaxation,  but  in  an  intermediate  condition 
between  relaxation  and  contraction.  The  object  of  this  is  to 
save  time ;  for  the  muscle  can  at  once  exert  its  power,  as  it 
has  no  "  slack  "  to  gather  in  before  it  exerts  its  pull.  Also 
there  is  no  jerk  or  jar  in  the  motion. 

Results  of  contraction  :  (a)  heat ;  (6)  motion  ;  (c)  sound  ;  (d) 
change  of  shape  ;  (e)  fatigue  ;  (/)  chemical  changes ;  (</)  rise 
of  electrical  state. 

Nerve-muscle  preparation — conditions  influencing  the  results  : 
(a)  freshness  of  the  nerve-muscle  preparation ;  (6)  suitable 
temperature  (98.6°  F.)  and  moisture  ;  (c)  suitable  stimulus — 
interrupted  electrical  current ;  (d)  moderate  weight  for  the 
muscle  to  act  on ;  (e)  duration  of  stimulus — not  less  than 
0.0015  of  a  second;  (/)  position  of  electrodes — they  must  be 
applied  to  the  nerve  obliquely  and  not  at  right  angles ;  (g)  a 
suitable  length  of  nerve  must  intervene  between  the  two 
electrodes. 

Nerve-muscle  preparation — order  of  fatigue :  Fatigue  ap- 
pears in  a  nerve-muscle  preparation :  first,  in  the  nerve- 


158  MUSCLE. 

endings  ;  second,  in  the  muscle-fibres ;  third,  in  the  nerve 
proper  (practically  untiring). 

The  following  experiments  are  offered  in  proof  of  the 
above  statement : 

Stimulate  a  nerve-muscle  preparation  through  the  nerve 
until  the  muscle  no  longer  contracts.  Then  apply  the  stimulus 
to  the  muscle-substance  directly  ;  it  is  noted  that  the  mus- 
cle is  excited  to  still  further  activity.  This  shows  that 
either  the  nerve  or  the  nerve-endings  were  exhausted  before 
the  muscle  itself.  To  determine  which  is  more  liable  to 
give  out,  nerve  or  nerve-endings,  perform  the  following 
experiment : 

Poison  a  nerve-muscle  preparation  with  curare,  which,  as 
has  been  shown  elsewhere,  inhibits  the  action  of  the  nerve- 
endings.  Now,  while  the  nerve-endings  are  paralyzed,  apply 
a  continuous  stimulation  to  the  nerve-fibre.  No  muscular 
activity  is  seen,  for  the  stimulus  cannot  pass  from  the  nerve 
to  the  muscle  across  the  bridge  of  poisoned  end-plates. 
Nevertheless  the  nerve  is  being  constantly  stimulated.  After 
a  time  the  effects  of  the  poison  pass  off  and  the  end-plates 
recover  their  activity,  and  the  stimulus  which  is  applied  to 
the  nerve  is  transmitted  to  the  muscle  and  active  contractions 
follow.  This  shows  that  the  nerve  outlasts  either  the  end- 
plates  or  muscle,  for  the  nerve  has  been  receiving  and  has 
been  capable  of  transmitting  stimuli  during  the  entire  stimula- 
tion, a  period  of  time  far  greater  than  that  during  which  either 
the  end-plates  or  muscle-fibre  would  have  been  capable  of 
such  activity. 

From  these  two  experiments  we  deduce  the  order  of  fatigue 
— (1)  nerve-endings,  (2)  muscle,  (3)  nerve-fibre.  It  is  also 
shown  that  nerve-fibre  is  practically  untiring. 

Rigor  mortis:  When  an  animal  dies  the  muscles  of  the 
body  do  not  die  at  once,  but  remain  alive  for  a  variable  time. 
In  man,  if  the  individual  be  wasted  and  enfeebled  by  luiiir 
illness  and  disease,  the  muscles  may  die  in  about  ten  minutes 
after  the  death  <>f  the  individual.  In  robust,  healthy  people 
>ii(l«leuly  killed,  the  muscles  may  live  for  six  or  eight  hours 
longer.  All  the  intermediate  stages  have  been  noted.  The 
death  of  the  muscle  is  characterized  by  a  contraction,  fixing 


MEDULLATED  FIBRES.  159 

the  limbs  and  body  in  a  rigid  condition.  This  post-mortem 
rigidity  constitutes  rigor  mortis.  The  muscles  of  the  jaw 
and  neck  are  usually  first  affected,  and  then  the  arm,  trunk, 
thighs,  and  legs  in  the  order  named.  All  muscles  are 
affected,  both  the  voluntary  and  involuntary. 

The  condition  of  rigor  mortis  lasts  from  ten  to  twenty- 
four  hours,  and  passes  off  in  the  inverse  order  from  its  ap- 
pearance. First  the  legs  relax,  then  the  thighs,  etc.,  and 
lastly  the  jaw. 

Cause  of  rigor  mortis  :  Rigor  mortis  is  caused  by  a  fermen- 
tative change  which  produces  a  coagulation  of  the  blood- 
plasma  in  the  muscles.  During  this  coagulation-process 
there  is  a  development  of  heat,  which  causes  a  rise  in  the 
temperature  of  the  body.  It  may  amount  to  5°  or  10°  F., 
or  even  more. 

Cause  of  disappearance  of  rigor  mortis  :  After  the  fermenta- 
tive change  which  causes  the  coagulation  of  the  muscle- 
plasma  has  ceased,  a  putrefactive  process  is  set  up  which 
destroys  the  coagulum  and  the  muscles  become  soft  and 
flabby. 

NERVOUS  SYSTEM. 

Fibres  and  Cells. 

The  nervous  system  is  an  aggregation  of  tissues  so  arranged 
as  to  adjust  the  workings  of  all  the  parts  of  the  body  to  one 
another  and  to  suit  the  body  to  its  environment. 

The  elementary  tissues  of  the  nervous  system  are  of  two 
forms  :  nerve-fibres  and  nerve-cells. 

The  nerve-fibres  are  of  two  kinds  :  (1)  medullated  or  white 
fibres ;  (2)  non-medullated  or  gray  fibres.  The  fibres  are 
united  in  bundles  to  form  nerve-trunks  or  "  nerves/' 

The  cells  are  in  groups  to  form  nerve-ganglia,  but  nerve- 
fibres  are  also  found  in  the  ganglia. 

Medullated  fibres  consist  of  (1)  an  external  nucleated 
sheath,  or  neurilemma  ;  (2)  an  inner  protective  medullary 
sheath  (the  white  matter  of  Schwann) ;  and  (3)  internally  the 
axis-cylinder  (Fig.  80). 


160 


NERVOUS  SYSTEM. 


The  neurilemma  is  a  pellucid   structureless  mem- 
brane.    Within  are  seen  at  inter- 
vals  nuclei   surrounded   by   more  FIG.  80. 
or  less  protoplasm.     These  nuclei 
and    their    protoplasm    are    relics 
of  embryonic  cells. 

The  medullary  sheath  is  a  thick 
fatty  semifluid  substance.  It  is 
this  substance  which  produces  the 
peculiar  white  appearance  of  some 
nerves.  Some  authorities  have 
claimed  that  it  is  made  up  of  a 
fine  network,  in  the  meshes  of 
which  is  embedded  the  bright 
fatty  material. 

The  axis-cylinder  consists  of  a 

large  number  of  primitive  fibrill*   Medullatcd  ncr"librc. 
which  vary  considerably  in  size,      A,  node  of 
but  on  the  average  may  be  said 
to  be  about  Y^j-ytn  inch  in  diam- 
eter.     There  is  little  doubt  that 
the  axis-cylinder  is  the  essential 
part  of  the  fibre,  the  other  parts 
being  merely  for  support  or  pro- 
tection. 

Nodes  of  Panvicr:  Here  and 
there  at  short  intervals  along  the 
course  of  medu Hated  fibres  are 
found  notches  or  constriction  in 
the  medullary  sheath.  These  con- 
strictions are  called  the  nodes  of  Ranvier.  At  these 
points  there  is  no  loss  of  continuity  of  the  axis- 
cylinder  nor  of  the  neurilemma,  but  the  medullary 
sheath  is  deficient  and  allows  the  neurilemma  to  dip 
in  and  touch  the  axis-cylinder. 

The  nodes  apparently  divide  the  nerve-fibre  off 
into  histological  units,  for  there  is  a  nucleus  for  each 
segment  marked  off  by  the  nodes. 

As  the  medullated  nerves  near  their  terminations, 


B,  nucleus  beloiii:in£ 
to  the  neurileinma  :  ('. 
axis-cylinder  ;  J'.  neu- 
rilemma  rendered  dis- 
tinct by  the  retraction 
of  the  myelin  of  the 
medullary  sheath.  In 
the  right-hand  figure 
the  clefts  of  LimtLT- 
mann  arc  shown  as 
while  lines  in  the 
dark  myelin.  The  fi^r- 
arefl  are  taken  from  spe- 
cimens treated  with 
osmic  acid,  which 
colors  the  tatty  con- 
stituents of  the  myelin 
a  dark  brown  or  black 
(Key  and  Retzius). 


FUNCTION  OF  NERVE-FIBRES. 


161 


FIG.  81. 


the  medullary  sheath  disappears  and  the  axis-cylinder  con- 
tinues with  the  neurilemma ;  but  this  latter  also  disappears 
before  the  final  ending  of  the  fibre  (axis-cylinder)  in  the 
tissues.  The  fibre  then  splits  into  two  or  more  terminal 
branches.  Thus  white  fibre  becomes  non-medullated  fibre. 

Non-medullated  fibres:  They  consist  of  the  axis-cylinder 
alone,  without  the  medullary  sheath.  They  do  not  differ  in 
any  other  regard  from  the  white  fibres.  When  collected 
in  bundles  to  form  nerves  they  have  a  yellowish  or  grayish 
color.  They  are  found  in  the  olfactory  and  auditory  nerves 
and  in  the  nerves  of  the  sympathetic  system,  and  they  occur 
in  greater  or  less  number  in  the  nerves  of  the  cerebro-spinal 
system.  In  size  these  fibres  are  about  one-third  to  one-half 
the  diameter  of  the  medullated.  They 
are  sometimes  spoken  of  as  the  fibres  of 
Remak  (Fig.  81). 

Formation  of  nerve-trunks :  To  build 
up  a  nerve-trunk,  whether  from  medul- 
lated or  non-medullated  fibres,  the  fibres 
are  joined  in  bundles  which  are  enclosed 
in  a  thin  fibrous  sheath  (perineurium), 
and  these  bundles  of  nerve -fibres  are 
bound  in  a  firm  connective-tissue  which 
serves  to  protect  and  to  unite  them 
strongly.  So  far  as  we  can  see,  the 
individual  nerve-fibres,  as  a  rule,  are 
continuous  and  independent  from  their 
origin  in  the  nervous  centres  to  within  a 
short  distance  of  their  peripheral  termi- 
nation. When  a  nerve  divides  into 
several  branches,  or  when  adjacent  nerves 
communicate,  it  is  because  certain  fibres 
leave  those  with  which  they  are  associ- 
ated and  pursue  a  different  course.  There 
is  no  real  union  of  nerve-fibres. 

Function  of  nerve-fibres :  The  function 
of  a  nerve-fibres  is  the  transmission  of  a 
stimulus.       The   axis-cylinder  connects  the   centre  and  pe- 
riphery cells,  and  conveys  between  them  the  stimuli.     This 

11— Phys. 


Fibres  of  Remak;  mag- 
nified 300  diameters. 
With  the  gelatinous 
fibres  are  seen  two  of 
the  ordinary,  dark 
bordered  nerve-fibres 
(Robin). 


102  NERVOUS  SYSTEM. 

transmission    for   any    particular   fibre   is   in    one   direction 

only. 

Depending  on  the  direction  the  impulse  is  carried,  the 
nerve-fibres  are  classified  into  afferent  (or  centripetal),  effer- 
ent (or  centrifugal),  and  intercentral  fibres. 

The  former  are  those  by  which  impressions  are  taken  from 
the  periphery  to  the  brain,  and  are  commonly  called  sensory 
fibres. 

Conduction  in  these  nerves  may  cause  (1)  a  sensation  as  of 
pain,  heat,  etc. ;  (2)  special  sensation ;  (3)  reflex  action  of 
some  kind  ;  or  (4)  inhibition  or  restraint  of  action. 

The  second  class  conduct  stimuli  to  the  periphery,  and  are 
known  as  motor  fibres.  Conduction  in  these  nerves  may 
cause  :  (1)  contraction  of  muscles  (motor  nerves) ;  (2)  control 
of  nutrition  (trophic  nerves) ;  (3)  control  of  secretion  (secre- 
tory nerves ;  or  (4)  inhibition,  augmentation,  or  checking  of 
other  efferent  impulses. 

The  last  class  includes  nerve-fibres  which  connect  more  or 
less  distinct  nerve-centres,  and  may  therefore  be  said  to  have 
no  peripheral  distribution.  Nerve-fibres  are  mere  conductors 
of  impressions.  An  impulse  started  in  any  fibre  is  trans- 
mitted unchanged  to  its  termination  without  being  imparted 
to  any  of  the  fibres  lying  near  it. 

Nerve-cells :  As  has  been  shown,  the  nerve-fibres  are  the 
conveyors  of  impulses,  either  from  the  brain  to  the  periphery, 
or  from  the  periphery  to  the  brain.  It  is  now  in  order  to 
study  the  termination  or  starting-points  of  these  impulses. 
Every  nerve-fibre  starts  or  ends  in  a  nerve-cell,  which  is  the 
origin  of  the  impulse  in  the  case  of  an  efferent  nerve-fibre,  or 
the  recipient  of  the  sensation  in  afferent  nerves. 

Nerve-cells  or  ganglion-cells  present  a  great  variety  of 
shapes,  and  yet  have  common  characteristics.  The  cell-body 
is  granular,  and  contains  a  large  nucleus  which  contain-  a 
prominent  nucleolus.  The  cells  have  at  least  one  pn»cos, 
and  often  more  (Fig.  82),  and  the  cells  are  classified  as  uni- 
polar, bipolar,  or  multipolar.  These  processes  are  of  two  kinds 
— one  kind  dividing  and  subdividing  (branching  or  proto- 
plasmic processes ;  or  dendrites)  until  they  become  very  deli- 
cate and  seem  to  interlace  with,  but  without  joining,  the 


NERVE-ENDINGS  AT  PERIPHERY. 


163 


equally  fine  processes  from  other  cells  ;  another  kind  (axis- 
cylinder  processes  or  axons)  pass  on  without  division  and  be- 
come axis-cylinders  of  medullated  nerve-fibres. 

The  nerve-cells  vary  greatly  in  size,  and  are  very  diverse 
in  form,  but  the  presence  of  a  nucleus,  a  nucleolus  and  the 
processes  is  characteristic  of  nerve-cells.  They  may  be 

FIG.  82. 


Is  from  the  anterior  horn  of  the  gray  substance  of  the  spinal  cord. 


enclosed  in  a  delicate  capsule,  which  becomes  continuous  with 
the  netiri lemma  (Fig.  83). 

Nerve-endings  at  periphery :  Efferent  nerves,  as  has  been 
stated  previously,  on  nearing  their  terminations  undergo  a 
loss  of  the  neurilemma  and  the  sheath  of  Schwann,  the  axis- 
cylinder  itself  splitting  into  several  subdivisions.  Each  of 
these  subdivisions  ends  directly  in  the  substance  of  a  cell  be- 
longing to  the  organ  supplied,  by  means  of  end- plates. 

Sensory  nerves  "  ending"  in  the  skin  find  their  way  to  or 
take  origin  from  certain  bodies  (sense-organs)  which  are  essen- 
tial to  the  conduction  of  the  sensory  impression  to  the  central 
nerve-ending.  These  sense-organs  are  of  several  kinds.  In 


NERVOUS  SYSTEM. 

the  fingers  and  toes  are  found  two  kinds  of  sense-organs 
which   may   be   especially    mentioned  :    1,    touch-corpuscles 


FIG.  83. 


Nerve-cells,  from  spinal  and  sympathetic  ganglia  of  man,  enclosed  in  their  cap- 
sular  sheaths— from  hardened  preparations  (Key  and  Rctzius). 


(Fig.  85);  2,  Pacinian  corpuscles  (Fig.  84).  The  exact 
anatomy  and  physiological  use  of  these  bodies  are  still  some- 
what obscure;  and,  indeed,  the  whole  subject  of  sensorv 
nerve-terminations  is  but  ill  understood.  We  may  regard 
the  fibres  of  sensory  nerves,  as  a  majority,  as  forming  a 
minute  plexus  in  the  corium  and  to  terminate  in  sense- 
organs  in  a  way  not  always  known.  Some  of  the  speeial 
sense-organs  are  possessed  of  nerve-endings  which  are  more 
clearly  observed. 

Neuron :   By  the  term  neuron  (Fig.  80)  is  meant  a  nervous 


NATURE  OF  NERVE-JM PULSE. 


165 


entity — that  is,  a  nerve-cell,  its  axis-cylinder  process,  dendrites, 
and  the  terminals. 

Nature  of  nerve-impulse :  The  nature   of  the  impulse  that 
travels  along  the  nerve  is  hard  to  determine.     Nerve-fibres 


FIG.  84. 


FIG.  85. 


A,  tactile  corpuscle ;  b,  nerve  (Quain). 

may  be  stimulated  by  any- 
thing which  increases  their 
irritability  with  sufficient 
suddenness,  but  they  cannot 
of  themselves  originate  such 
a  condition.  The  stimulus 
produces  its  effect  upon  the 
nerve-termination.  The  re- 
sult, therefore,  of  any  stimu- 
lation of  a  nerve  depends 
solely  on  the  character  of  the 
end-organ,  and  not  upon  the 
character  of  the  stimulus. 

Artificially  in  a  nerve-mus- 
cle preparation  the  impulse 
can  be  aroused  by  four  meth- 
ods :  chemical,  thermal,  electrical,  and  mechanical  means. 
The  impulse  passing  along  the  nerve  is  not  chemical,  be- 
cause there  is  no  heat  liberated  ;  nor  is  there  an  expansion 
of  nerve-fibre,  even  after  prolonged  activity,  and  naturally 
one  would  expect  heat  and  expansion  as  the  result  of  chemi- 


Vater's  or  Pacini's  corpuscle,  a,  stalk  ; 
b,  nerve-fibre  entering  it ;  a,  d,  con- 
nective-tissue envelope ;  e,  axis- 
cylinder,  with  its  end  divided  at  / 


S 


(Quain). 


166 


NERVOUS  SYSTEM. 


Fro.  86. 


Neuron  with  long  axon  proceeding  as  an 
uxis-cyliiiderof  a  nerve-fibre,  n,  nerve- 
cell  proper  ;  r/,dendrites  ;  x,  axon ;  d.  g., 
dendrite  showing  gemmulee;  c,  collutt  r 
als;  /•.  nui  tut'ts  or  terminals.  Pyram- 
i<lul  cell  of  the  cerebral  cortex  (S. 
Ramon  y  Cajal). 


cal  changes.  The  fact  that 
the  nerve  does  not  change 
its  temperature  excludes 
the  thermal  theory. 

The  impulse  cannot  be 
an  electrical  one,  because 
there  is  no  insulation  for 
the  conductors  (the  nerves). 

The  best  explanation  of 
the  impulse  is  that  prob- 
ably it  is  a  physical  molec- 
ular vibration. 

Direction  of  nerve  -  im- 
pulse :  A  nerve  -  impulse 
may  travel  in  either  direc- 
tion in  a  given  nerve,  be 
it  either  afferent  or  effer- 
ent;  but  the  impulse  trav- 
elling in  the  physiological 
direction  alone  is  manifest, 
because  the  impulse  travel- 
ling in  the  physiological  di- 
rection is  the  only  one  that 
finds  suitable  terminals 
through  which  to  become 
manifest. 

It  can  be  shown  that  a 
nerve-fibre  is  capable  of 
transmitting  its  impulse  in 
either  direction  by  the  fol- 
lowing experiments : 

1.  Take  a  fresh  nerve 
of  considerable  length,  and 
apply  near  its  middle  tin- 
two  polos  of  a  galvanom- 
eter. Apply  a  suitable 
stimulus  to  one  end  of  the 
nerv<-  ;  an  impulse  will  be 
generated  which  will  travel 


DEGENERATION.  167 

along  the  nerve.  The  presence  of  the  impulse  will  be  de- 
tected by  the  galvanometer.  This  change  of  electrical  state, 
due  to  the  physical  molecular  vibrations  and  shown  by  the 
^alvanometer,  is  called  the  "current  of  action."  The  gal- 
vanometer has  now  shown  that  the  nerve  has  carried  an  im- 
pulse in  one  direction.  If  now  we  apply  the  stimulus  to  the 
opposite  end  of  the  nerve,  the  galvanometer  again  will  record 
a  "  current  of  action,"  thus  showing  an  impulse  travelling  in 
the  opposite  direction  to  that  taken  by  the  first  impulse. 

2.  If  one  were  to  stimulate  one  of  the  terminal  branches 
f  an  efferent  axis-cylinder,  not  only  would  the  impulse 
travel  in  the  physiological  direction  toward  the  end-organ, 
but  the  impulse  would  travel  up  the  branch  of  the  axis- 
cylinder  until  it  reached  the  point  where  the  axis-cylinder 
had  divided,  and  then  travel  down  the  other  branches  to 
their  respective  end-organs. 

Speed  of  nerve-impulses :  Efferent  impulses  are  somewhat 
slower  than  afferent,  the  rate  for  the  former  being  about  110 
feet  per  second  ;  for  the  latter,  about  150  feet. 

The  time  occupied  in  executing  a  voluntary  movement  at 
a  given  signal — for  instance,  the  recording  the  time  of  a 
transit  in  an  astronomical  observation — is  found  to  be  suffi- 
cient to  demand  a  correction  for  an  accurate  result.  This 
amounts  to  ^  to  -fa  of  one  second  with  different  individuals. 
The  time  lost  in  this  way  is  known  as  the  personal  error  of 
the  observer.  When  this  has  been  ascertained  by  experi- 
ment, the  allowance  to  be  made  for  the  personal  error  is  his 
personal  equation.  This  remains  nearly  constant  for  each 
person. 

Degeneration :  When  a  nerve  is  divided  its  function,  of 
course,  ceases.  It  is  no  longer  capable  of  carrying  impulses 
throughout  its  length,  owing  to  the  loss  of  continuity.  But 
by  applying  proper  artificial  stimulation  to  the  nerve  at  a 
point  distal  to  the  point  of  division  in  the  case  of  an  efferent 
nerve,  or  proximal  to  the  cut  in  an  afferent  nerve,  a  response 
is  obtained  similar  to  the  normal  action.  For  example, 
certain  muscles  may  be  made  to  contract  by  applying  an 
electric  shock  to  the  distal  end  of  a  cut  motor  nerve ;  or 
sensation  of  pain  may  be  produced  by  stimulating  the  proxi- 


O\^llk5Cl 


168  NERVOUS  SYSTEM. 

mal  end  of  a  sensory  nerve.  Furthermore,  it  is  noticed  that 
for  the  first  few  hours  after  division  the  irritability  of  a 
divided  nerve  is  heightened  ;  after  this  period  of  heightened 
irritability  the  nerve  begins  to  lose  its  power  of  conductivity, 
and  in  three  or  four  days  the  process  of  degeneration  is  com- 
plete and  the  nerve  fails  to  convey  any  impulses. 

Microscopic  examination:  When  examined  under  the  micro- 
scope a  divided  nerve-fibre  presents  certain  changes.  At  the 
point  of  division,  degeneration  takes  place  in  but  one  direc- 
tion, and  that  away  from  the  "  nutrient  cell,"  or  cell  of  which 
it  was  an  outgrowth.  The  degeneration  of  the  fibre  extends 
to  its  final  distribution.  In  the  case  of  a  medullated  nerve- 
fibre,  if  the  section  is  at  a  point  between  two  nodes  of  1  Jan- 
vier, the  degeneration  in  that  portion  of  the  nerve  still  in 
continuity  with  its  trophic  cells  extends  up  as  far  as  the  first 
node  of  Ranvier  from  the  point  of  section. 

The  histological  changes  during  the  period  of  degeneration 
are  as  follows  :  During  the  period  of  increased  irritability  the 
axis-cylinder  is  slightly  granular,  and  the  medullary  sub- 
stance somewhat  cloudy.  Soon  a  complete  fragmentation  of 
the  axis-cylinder  takes  place,  the  myelin-substance  is  de- 
stroyed, the  axis-cylinder  is  absorbed,  and  in  place  of  the 
normal  nerve  only  the  neurilemma  is  left. 

Non-mod ul lated  fibres  have  not  been  studied  with  such 
great  care,  but  the  process  of  degeneration  is  the  same  as 
that  described,  except  for  the  absence  of  a  medullary 
substance. 

The  degeneration  occurs  practically  simultaneously  through- 
out the  entire  portion  of  the  nerve  involved. 

Nerve-regeneration:  If,  under  proper  precautions,  the  sev- 
ered ends  of  a  divided  nerve  are  put  in  apposition,  they  may 
be  made  to  unite  and  regenerate,  with  a  return  of  function. 
1 1  is  noticed  that  sensory  fibres  regenerate  more  rapidly  than 
motor — i.e.,  in  the  ease  of  an  ordinary  mixed  somatic  nerve 
during  regeneration  pain  is  felt  before  motion  is  present. 

Microscopic  examination  shows  an  extension  of  the  axis- 
cylinder  from  the  normal  part  of  the  nerve  into  the  empty 
neurilemma  of  the  degenerated  portion.  The  regenerating 
:i\i— cylinder  extends  along  until  it  reaches  the  final  distrilm- 


SYMPATHETIC  SYSTEM.  169 

tion  of  the  nerve,  the  medullary  substance  gradually  being 
reformed,  until  the  nerve  is  again  intact. 

Although  the  nervous  system  throughout  the  body  is  con- 
nected with  the  brain  and  forms  an  integral  whole,  neverthe- 
less it  has  always  been  the  custom  to  speak  of  a  certain  por- 
tion of  the  nervous  system  as  a  separate  part,  to  which  the 
name  "  sympathetic  system  "  has  been  given,  the  rest  of  the 
nervous  system  being  designated  as  the  cerebro-spinal. 

The  cerebro-spinal  system  consists  of  the  brain,  the  medulla 
oblongata,  and  the  spinal  cord,  with  the  nerves  proceeding 
from  them. 

Sympathetic  System. 

Primarily,  the  sympathetic  system  (Fig.  87)  consists  of  a 
double  chain  of  ganglia  and  communicating  nerves  which  lie 
on  either  side  of  the  vertebral  column  and  extend  throughout 
its  entire  length.  Other  ganglia  occur  in  connection  with 
some  of  the  cranial  nerves,  more  especially  the  vagus  and 
trigeminus.  There  are  ganglia  and  plexuses  connected  with 
the  various  organs  (e.  </.,  cardiac  and  solar),  and  still  others 
in  the  substance  of  some  of  the  organs  (e.  g.,  stomach  and 
intestines) ;  still  others  in  connection  with  the  bloodvessels. 
The  sympathetic  system  has  numerous  communications  with 
the  cerebro-spinal  system. 

The  fibres  of  the  sympathetic  nerves  are  often  smaller  than 
those  of  the  cerebro-spinal  system,  and  among  them  are  a  large 
number  of  non-medullated  fibres.  The  sympathetic  nerves  do 
not  differ  materially  from  the  cerebro-spinal.  They  are  very 
similar.  The  occurrence  of  ganglia  upon  the  sensory  branches 
of  the  spinal  nerves  and  upon  the  sensory  cranial  nerves 
(pneumogastric,  glosso-pharyngeal,  and  trigeminus)  adds  to 
the  similarity.  Then,  too,  the  frequent  communications  be- 
tween the  two  systems  practically  make  one  system  of  them, 
and  the  division  is  largely  one  for  convenience. 

Communication  of  cerebro-spinal  and  sympathetic  systems  : 
From  each  spinal  nerve  is  given  off  a  communicating  branch 
to  a  neighboring  sympathetic  ganglion.  These  branches  con- 
tain both  motor  and  sensory  fibres.  Thus  it  is  seen  that  all 


170 


NERVOUS  SYSTEM. 
FIG.  87. 


Ganglia  and  nerves  of  the  sympathetic  system. 


impulses  travelling  alon^  the  sympathetic  system  may  cither 
start  or  terminate  in  the  cerebro-spinal. 


CEPHALIC  GANGLIA.  171 

By  the  term  ganglion  is  meant  a  collection  of  gray  and 
white  nerve-substance,  which  is  usually  oval  in  outline,  and 
is  frequently  found  in  the  course  of  a  nerve-trunk.  In  the 
sympathetic  system  the  ganglia  contain  numerous  nerve-cells, 
smaller  than  those  of  the  brain  and  spinal  cord,  and  from 
these  cells  arise  nerve-fibres  which  distribute  themselves  in 
the  plexuses. 

Ganglia  of  the  sympathetic.  The  long  chain  of  ganglia, 
with  the  various  plexuses,  of  the  sympathetic  system  are 
classified  regionally  as  cephalic,  cervical,  thoracic,  abdominal, 
and  pelvic  ganglia  and  plexuses. 

Cephalic  ganglia  :  In  the  head  the  sympathetic  ganglia  are 
four  iu  number — ophthalmic,  spheno-palatine,  submaxillary, 
and  otic  ganglia.  Each  has  communications  from  the  general 
sympathetic;  and  from  the  cranial  nerves  both  motor  and  sen- 
sory fibres. 

Ophthalmic  ganglion:  It  is  a  small  ganglion  situated  in  the 
orbit,  and  receives  communications  from  the  sympathetic  and 
from  the  motor  oculi  (third)  nerve,  a  motor  branch,  and  from 
the  trigeminus  (fifth)  nerve  a  sensory  branch.  Its  branches 
pass  into  the  eyeball  (ciliary  nerves),  and  are  distributed  in 
the  iris.  Their  function  is  the  control  of  the  pupil,  of  the 
apparatus  of  accommodation,  and  of  the  vaso-motor  function 
in  the  vessels  of  the  eye. 

Spheno-palatine  ganglion :  It  is  situated  in  the  spheno-max- 
illary  fossa,  and  receives  branches  from  the  cervical  sympa- 
thetic system  and  motor  fibres  from  the  facial  (seventh)  nerve, 
and  sensory  from  the  fifth.  Its  branches  are  distributed  to 
the  mucous  membrane  and  muscles  of  the  palate  and  uvula, 
and  to  the  naso-pharynx.  They  are  both  sensory  and  motor. 

The  submaxillary  ganglion  lies  in  close  proximity  to  the 
submaxillary  gland.  It  receives  branches  from  the  superior 
cervical  ganglion  by  way  of  the  plexus  on  the  facial  artery, 
and  a  sensory  branch  from  the  lingual  branch  of  the  fifth 
nerve.  Its  motor  branch  is  through  the  chorda  tympani 
nerve  from  the  seventh  or  facial  nerve.  Its  branches  are 
distributed  to  the  submaxillary  gland  and  control  its 
function. 

The  otic  ganglion  is  a  small  ganglion  lying  upon  the  third 


172  NERVOUS  SYSTEM. 

division  of  the  fifth  nerve  as  it  emerges  from  the  foramen 
ovale.  It  has  branches  from  the  sympathetic  on  the  middle 
meningeal  artery,  and  both  a  motor  and  a  sensory  communi- 
cation from  the  fifth,  as  well  as  a  branch  from  the  glosso- 
pharyngeal  through  Jacobson's  nerve.  Its  branches  are 
motor,  to  the  tensor  palati  and  tensor  tympani  muscles ;  and 
sensory,  to  the  mucous  membrane  of  the  tympanum  and 
Eustachian  tube. 

Cervical  ganglia:  There  are  two— a  superior  and  an  in- 
ferior (with  sometimes  a  third,  middle) — ganglia  on  each  side 
(Fig.  87).  These  ganglia  receive  communications  from  each 
of  the  cervical  spinal  nerves  and  from  each  other.  Their 
branches  are  given  off:  (1)  to  form  the  carotid  plexus,  which 
follows  the  carotid  artery  and  its  branches,  forming  by  its 
inosculations  the  vaso-motor  plexuses  of  the  carotid  system. 
(2)  To  furnish  branches  for  distribution  to  the  thyroid  gland, 
larynx,  trachea,  pharynx,  and  oesophagus.  (3)  To  form  the 
cardiac  nerves,  which  are  distributed  in  the  cardiac  plexus. 

Thoracic  ganglia :  In  the  chest  the  ganglia  are  numerous 
(Fig.  87),  and  each  ganglion  receives  two  branches  of  com- 
munication from  the  intercostal  nerve  above  it,  while  the 
relationship  of  the  ganglia  is  maintained  by  the  intercommu- 
nicating chain.  The  nerves  originating  here  are  distributed 
to  the  plexuses  on  the  thoracic  aorta,  and  to  those  of  the 
lungs  and  oesophagus. 

Abdominal  ganglia :  In  the  abdomen  there  is  an  aggrega- 
tion of  ganglionic  enlargements  situated  upon  the  co-liae 
artery,  known  as  the  semilunar  or  cceliac  ganglion.  It  com- 
municates with  the  thoracic  ganglia  and  with  all  the  lumbar 
nerves.  From  this  centre  proceed  a  multitude  of  diverging 
and  inosculating  fibres,  which,  from  their  common  origin  and 
radiating  course,  are  called  the  solar  plexus.  Its  secondary 
plexuses,  accompanying  the  branches  of  the  abdominal  aorta, 
are  distributed  to  'the  stomach,  intestines,  spleen,  pancreas, 
liver,  kidney,  and  internal  organs  of  generation. 

Pelvic  plexuses:  The  plexuses  of  the  pelvis  are  derived 
from  four  or  five  pairs  of  ganglia  situated  on  the  anterior 
portion  of  the  sacrum  and  terminating  in  the  ganglion  i))i}><tr, 
lying  upon  the  coccyx.  Its  fibres  join  those  from  the  solar 


VASO-MOTOR  FIBRES.  173 

plexus,  and  are  distributed  with  them  along  the  course  of 
the  branches  of  the  internal  iliac  arteries. 

Sympathetic  system — function:  The  action  of  the  sympa- 
thetic is  principally  shown  in  the  organs  of  nutrition  and 
secretion  and  in  the  vascular  system.  The  sympathetic  also 
plays  an  important  part  in  the  special  senses — e.  g.,  dilatation 
of  the  pupil  is  effected  through  it,  and  probably  accommoda- 
tion is  acted  upon  by  fibres,  other  than  the  oculomotorius, 
which  come  through  the  lenticular  ganglion.  The  tensor  tym- 
pani  muscle  is  supplied,  indirectly,  from  the  otic  ganglion. 
The  efferent  nerve-fibres  of  the  sympathetic  system  send  to 
the  muscles  of  the  vascular  system  vaso-motor  (i.  e.,  vaso- 
constrictor and  cardiac  accelerator)  and  also  vaso-inhibitory 
fibres  (i.  e.,  vaso-dilator  and  cardiac  inhibitory).  To  the 
muscles  of  the  viscera  they  send  both  vaso-motor  and  vaso- 
inhibitory  fibres. 

Sensory  and  motor  influence  of  the  sympathetic :  It  will  be 
remembered  that  the  spinal  nerves,  both  afferent  and  efferent, 
act  very  quickly  upon  the  tissues  supplied  by  them;  the 
sympathetic  nerves  act  more  slowly.  Thus,  if  the  afferent 
nerve  of  a  ganglion  or  its  efferent  nerve  be  stimulated,  there 
is  a  slow  wave-like  series  of  motions  set  up  in  the  parts  sup- 
plied, which  continue  for  some  time  after  the  stimulus  is  with- 
drawn. This  is  particularly  well  seen  in  intestinal  peristalsis, 
which  may  be  excited  by  stimulation  of  the  intestine  or  of 
the  semilunar  ganglion  or  of  the  branches  of  the  solar 
plexus. 

Relation  of  the  sympathetic  to  the  secreting  glands :  There 
has  been  demonstrated  in  some  of  the  secreting  glands — and 
it  is  probably  true  for  all — that  functional  stimuli,  distinct 
from  the  vaso-motor,  come  through  the  sympathetic  nerves, 
and  that  these  fibres  are  closely  associated  with  the  vaso- 
motor  fibres.  Thus,  in  the  stomach  the  secretion  of  the 
gastric  juice  is  only  temporarily  suspended  by  the  section  of 
the  vagi,  and  is  resumed  by  the  action  of  the  sympathetic, 
showing  that  the  control  is  by  the  sympathetic.  Thus  it  is 
seen  that  there  are  true  "  secretory  "  nerve-fibres. 

Vaso-motor  fibres  :  The  vaso-motor  function  of  the  sympa- 
thetic has  been  discussed  under  the  section  on  Circulation. 


174 


NERVOUS  SYSTEM. 


Transverse  sections  of 
the  sjiiiiiil  cord  in  man. 
I,  upper  cervical  re- 
gion :  II,  lower  cervical 
region;  III.  dorsal  re- 
gion :  IV,  lumbar  en- 
largement ;  V,  lower  ex- 
tremity. 


Spinal  Cord. 

Gross  anatomy :  The  spinal  cord  is 
that  portion  of  the  cerebro-spinal  nerv- 
ous system  contained  within  the  spinal 
canal.  It  connects  with  the  medulla 
oblongata,  and  terminates  in  a  fine 
thread  of  gray  matter  (the  filum  termi- 
nale)  at  about  the  second  lumbar  ver- 
tebra. In  form  it  is  irregularly  cylin- 
drical, and  varies  in  the  size  and  shape; 
of  its  cross-section  at  various  levels,  as 
is  shown  in  Fig.  88.  It  is  incompletely 
divided  into  symmetrical  halves,  and  its 
mid-line  is  indicated  in  front  by  a  fissure 
(anterior  median  fissure)  which  extends 
for  about  one-third  its  antero-posterior 
diameter;  behind  by  a  deeper  but  nar- 
rower fissure  (posterior  median  fissure), 
which  involves  about  one-half  of  the 
same  diameter.  It  is  composed  of  white 
and  gray  substance. 

Issuing  from  the  cord  along  its  course 
are  thirty-one  pairs  of  nerves.  Each  of 

FIG.  89. 


Transverse  section  of  tin- spinal  cord,  a,  t>, 
spinal  nerves  of  tin-  right  and  left  sides; 
(I,  origin  of  the  anterior  rout  :  e,  origin 
of  the  posterior  root ;  c,  ganglion  of  the 
posterior  root.' 


these  spinal  nerves  is  made  up  of  an  an- 
terior and  a  posterior  root  (Fig.  89),  of 
which  the  latter  is  the  larger.  The  ante- 
rior root  arises  between  the  anterior  and 
lateral  white  columns,  the  posterior  be- 


SPINAL  CORD.  175 

tween  the  posterior  and  lateral  columns.  On  each  pos- 
terior nerve-root  is  found  a  ganglion  immediately  beyond 
its  point  of  emergence.  The  function  of  this  seems  to  be 
trophic. 

The  white  substance  is  arranged  externally  to  the  gray  in 
each  half  of  the  cord,  and  is  so  disposed  as  to  be  conve- 
niently divided  for  purposes  of  description  into  three  columns, 
known  respectively  as  the  anterior,  lateral,  and  posterior 
columns  of  the  cord.  There  is  also  a  thin  band  of  white 
substance  at  the  base  of  the  anterior  median  fissure  (the 
white  commissure).  The  gray  matter  fills  in  the  central 
portion  of  the  cord,  and  is  variable  in  its  amount,  the  calibre 
of  the  cord  at  its  enlargements  being  increased  by  the  in- 
crease in  the  amount  of  gray  matter  at  these  points  (Fig.  88). 
The  white  substance  will  be  noticed  to  diminish  quite  regu- 
larly in  the  sections  of  the  cord  from  above  downward,  as 
seen  in  this  series.  The  gray  substance  is  not  completely 
halved  by  the  anterior  and  posterior  fissures  of  the  cord,  but 
is  continuous  across  the  mid-line  (gray  commissure) ;  and  in 
it  at  the  centre  is  a  minute  canal  communicating  with  the 
ventricles  of  the  brain.  The  gray  matter  is  more  abundant 
between  the  lateral  and  anterior  and  between  the  lateral  and 
posterior  columns  of  the  white  substance  ;  the  names  anterior 
and  posterior  horns  (cornua)  are  given  to  these  regions  re- 
spectively. 

Spinal  cord — microscopic  examination:  Under  minute  ex- 
amination the  white  matter  is  found  to  be  made  up  of  medul- 
lated  nerve-fibres,  which  collect  to  form  the  anterior  and 
posterior  nerve-roots,  and  communicate  with  other  regions 
of  the  cord. 

The  gray  matter  contains  multipolar  cells  of  varying  size 
and  shape,  with  axis-cylinders  and  "  branching77  processes 
lying  in  the  neuroglia  ("  connective  tissue ").  The  multi- 
polar  cells  are  some  of  them  quite  large.  In  the  anterior 
horn  of  the  gray  substance  the  axis-cylinder-processes  of  the 
nerve-cells  connect  directly  with  fibres  forming  the  anterior 
nerve-roots  (Fig.  90) ;  but  in  the  posterior  cornu  the  com- 
munication is  indirect — i.  e.,  through  the  branching  processes 
and  the  divided  axis-cylinders  of  the  collaterals  of  the  pos- 


176 


NERVOUS  SYSTEM. 


terior  nerve-roots,  forming  thus  by  contiguity  what  are  known 
as  end-arborization^. 

Origin  and  course  of  nerve-roots :  (a)  Anterior  nerve-roots 
are  derived  from  (1)  the  anterior  columns  of  the  cord,  but 
some  fibres  come  through  the  commissure  from  (2)  the  oppo- 
site side,  and  some  come  from  (3)  the  lateral  tract.  Still 
other  fibres  arise  from  (4)  the  multipolar  cells  in  the  anterior 
cornu  of  the  gray  matter.  The  fibres  of  the  anterior  nerve- 

Fio.  90. 


Transverse  section  of  the  spinal  cord  in  man  (lumbar  region). 

roots  are  efferent — i.  e.,  they  carry  impulses  from  the  centre 
(brain)  to  the  periphery. 

(/>)  Posterior  nerve-roots  give  off  collaterals  which  enter  the 
posterior  horn  of  the  gray  matter,  and  the  ultimate  fibres 
break  up  and  form  "indirect"  communication  with  the 
branching  processes  of  the  large  multipolar  cells,  but  some 
fibres  cross  through  the  gray  commissure  to  the  opposite  side. 
The  fibres  of  the  posterior  roots  arc  afferent — i.  e.,  they  cnrry 
impulses  from  the  periphery  to  the  centre  in  the  cord, 
medulla,  or  brain. 

The  course  of  all  the  fibres  through  the  cord  itself  has  not 
been  determined  with  absolute  accuracy.  Certain  fibres,  how- 


TROPHIC  CENTRES  OF  NERVE-ROOTS.  Ill 

ever,  have  been  traced  through  their  length,  notably  the  fibres 
of  the  pyramidal  tracts,  in  the  anterior  and  lateral  columns. 

It  has  been  calculated  that  only  about  one-half  as  many 
fibres  enter  the  spinal  cord  from  the  brain  as  leave  it  through 
the  nerves ;  therefore  it  must  follow  that  some  fibres  originate 
from  the  corcl.  The  increase  in  gray  matter  in  the  cervical 
and  lumbar  enlargements,  where  the  fibres  for  the  large  plex- 
uses of  the  nerves  (branchial  and  lumbar)  are  given  off,  con- 
firms this  view. 

Spinal  cord — recurrent  sensibility  fibres :  Certain  afferent 
fibres  in  the  nerve-trunks  of  the  body  do  not  pass  directly  into 
the  posterior  nerve-roots  and  so  to  the  spinal  cord,  but  take  an 
erratic  course  as  follows  :  After  leaving  the  nerve-trunk  these 
fibres,  known  as  the  recurrent  sensibility  fibres,  pass  into  the 
anterior  nerve-root,  being  mingled  with  the  efferent  fibres  fora 
short  distance  ;  then  these  fibres  double  on  their  course,  return 
to  the  point  of  junction  between  the  anterior  and  posterior 
nerve-roots,  to  follow  by  way  of  the  posterior  root  the  normal 
course  to  the  cord.  These  fibres  form  but  a  small  proportion 
of  the  afferent  fibres,  and  the  purpose  of  their  erratic  course 
is  not  easily  explainable. 

Trophic  centres  of  nerve-roots — degeneration  :  The  posterior 
nerve-roots  seem  to  be  dependent  upon  the  ganglia  which  are 
found  upon  them  for  trophic  influence.  The  anterior  root  in 
a  similar  way  seems  to  depend  upon  a  trophic  centre  in  the 
gray  matter  in  the  anterior  horn. 

Division  of  a  nerve  is  followed  by  a  degeneration  or  break- 
ing down  of  the  axis-cylinders  of  its  fibres  within  a  day  or 
two,  the  loss  of  function  being  an  earlier  and  immediate 
manifestation.  This  degeneration  is  centrifugal — that  is,  does 
not  proceed  toward  the  spine,  but  to  the  periphery.  If  the 
posterior  root  be  cut,  however,  between  its  ganglion  and  its 
emergence  from  the  cord,  the  degeneration  is  toward  the  cord 
— i.  c.,  centripetal — and  the  nerve  beyond  the  ganglion  does 
not  degenerate.  The  anterior  root  cannot,  however,  be 
divided  at  any  point  beyond  its  emergence  without  centrifugal 
degeneration  of  the  fibres  (Fig.  91).  The  regeneration  takes 
place  slowly  if  the  continuity  of  the  nerve  is  at  once  restored, 
and  may  even  follow  after  the  nerve  has  degenerated  for  some 

12— Phys. 


178 


NERVOUS  SYSTEM. 


months  and  a  complete  loss  of  function  has  affected  the  part 
supplied  by  it.  The  fact  that  the  axis-cylinders  are  restored 
only  in  this  way  is  of  interest,  as  showing  the  influence  of  the 
trophic  centres  on  the  nerve-growth. 


FIG.  91. 


Degeneration  of  spinal  nerves  and  nerve-roots  after  section.  A,  section  of  nerve- 
trunk  beyond  the  ganglion ;  B,  section  of  anterior  root ;  C,  section  of  posterior 
root ;  D,  excision  of  ganglion  ;  a,  anterior  root ;  p,  posterior  root ;  g,  ganglion. 

The  functions  of  the  spinal  cord  may  be  tabulated  as  fol- 
lows : 

(a)  Conduction,  or  carrying  impulses  between  centre  and 
periphery  ; 

(b)  Transference — i.   e.,  an   apparent    transferring  of   im- 
pression from  one  set  of  fibres  to  another ; 

(c)  Reflex  action — i.  e.,  the  origination  of  action  in  response 
to  stimuli  from  the  periphery ; 

(d)  Augmentation,  or  a  resulting  effect  in  excess  of  the 
exciting  cause; 

(e)  Automatic  acts,  from  corresponding  centres ; 

(/)  Coordination,  or  the  adjustment  of  the  workings  of 
different  parts  of  the  body  to  one  another; 

(g)   In  hi /tit  ion  of  reflex  acts. 

Conduction :  Than  by  the  spinal  cord  there  is  practically  no 
other  nervous  communication  between  the  brain  and  the 
musculo-cutaneous  system;  hence  through  it  must  conic  nil 
the  nerve-impulses  which  pass  to  or  from  the  brain.  In 
other  words,  every  sensory  impulse  that  is  felt  and  every 
motion  that  is  willed,  perception  and  volition  being  attributes 


CONDUCTION.  179 

of  the  brain,  must  be  conducted  through  the  nerve-fibres  of 
the  spinal  cord  to  the  brain,  and  vice  versa. 

The  student  must  not  suppose  that  in  all  instances  a  con- 
tinuous nerve-fibre  runs  from  the  central  cell  in  the  brain  to 
the  peripheral  end-organ,  and  vice  versa.  The  nerve-fibre  is 
often  broken  at  one  or  more  places  along  its  course,  the  end 
of  the  fibre  terminating  in  a  brush-like  ending  which  "  articu- 
lates "  with  the  dendrites  of  a  secondary  or  relay  cell.  The 
impulse  is  thus  communicated  to  the  second  cell,  which  in 
turn  transmits  the  impulse  along  its  own  nerve-fibre  and 
so  on. 

The  conducting  fibres  in  the  cord  lie  chiefly  in  the  white 
matter;  whereas  the  gray  substance  represents  the  cell-ele- 
ments as  well. 

The  conducting  fibres  have  definite  positions  in  the  cord, 
and  each  portion  has  fibres  which  always  conduct  the  same 
kind  of  impressions. 

Most  of  the  motor  fibres  cross  to  the  opposite  side  in  the 
medulla  oblongata  (decussation  of  the  pyramids),  and  the  im- 
pulses pass  down  by  the  lateral  columns  in  the  crossed  or  lat- 
eral pyramidal  tract  on  the  side  opposite  to  that  in  which  they 
originate.  There  is  also  a  set  of  motor  fibres  which  does  not 
cross,  but  passes  directly  to  the  same  side  in  the  anterior  col- 
umns, and  decussates  in  the  anterior  or  white  commissure  near 
the  point  of  distribution.  The  destination  of  these  fibres  is 
variable,  for  the  reason  that  the  amount  of  decussation  in  the 
medulla  is  not  constant ;  but,  as  a  rule,  the  fibres  in  the  direct 
tract  go  to  the  upper  portion  of  the  body.  The  cells  in  the 
anterior  cornu  of  the  gray  matter  of  the  cord  originate  many 
of  the  fibres  which  go  to  the  nerves.  This  is  demonstrated 
after  division  of  the  cord  by  stimulating  these  fibres :  a  series 
of  coordinated  motions  follows,  and  this  stimulus  may  be  ap- 
plied direct  to  the  fibres  or  through  the  sensory  nerves. 

The  course  of  the  sensory  fibres  (Fig.  92)  is  somewhat 
problematical,  but  certainly  these  impulses  enter  the  cord  by 
the  posterior  nerve-roots.  The  fibres  conducting  them  break 
up  as  described,  and  cross  to  the  opposite  side  of  the  cord 
through  the  gray  commissure.  It  is  probable  that  after  decus- 
sating the  fibres  communicate  with  multipolar  cells,  and  thus 


180 


NERVOUS  SYSTEM. 


pass  on  as  white  fibres  in  the  lateral  columns.  These  fibres 
after  entering  the  lateral  columns  (of  the  opposite  side)  pass 
to  the  medulla  as  a  distinct  tract — the  antero-lateral  ascending 


FIG.  92. 


Diagram  showing  pathway  of  the  sensory  impulses.  On  the  left  side  SS'  represent 
afferent  spinal  nerve-fihres ;  C,  an  afferent  cranial  nerve-fibre.  These  fibres  ter- 
minate near  central  cells,  the  neurons  of  which  cross  the  middle  line  and  end 
in  the  opposite  hemisphere  (Van  Gehuchten). 

tract — at  the  periphery   of  the  lateral,   extending  into  the 
anterior  column. 


REFLEX  ACTION.  181 

It  is  by  this  tract  that  sensations  of  pain  and  of  tempera- 
ture are  supposed  to  pass.  There  are  also  afferent  fibres  in 
the  posterior  columns — the  posterior  median — by  which  the 
sensations  of  touch  and  weight  (or  muscular  sensation)  are  be- 
lieved to  pass ;  the  latter,  however,  does  not  decussate.  To 
recapitulate :  sensations  of  pain  and  temperature  are  trans- 
mitted through  the  lateral  columns,  and  those  of  touch  and 
weight  through  the  posterior  columns. 

Transference  :  Impressions  conveyed  by  a  centripetal  nerve- 
fibre,  it  has  been  stated,  pass  uninterruptedly  throughout 
its  whole  length  without  being  communicated  to  adjacent 
fibres.  When  such  an  impression  reaches  a  nerve-centre  in 
the  cord,  it  may  seem  to  pass  to  another  fibre  or  set  of  fibres, 
so  that  the  pain  or  other  sensation  is  felt  in  an  entirely  differ- 
ent part  from  that  in  which  the  stimulus  started.  At  the 
same  time  the  primary  impression  may  also  be  conducted  to  the 
brain,  so  that  the  sensation  seems  to  come  from  two  different 
places.  This  phenomenon,  known  as  transference,  cannot  be 
well  explained,  yet  instances  of  it  are  very  frequent.  In  dis- 
ease of  the  hip  the  pain  is  frequently  felt  in  the  knee  alone, 
yet  the  latter  may  be  perfectly  sound.  A  biliary  calculus 
will  often  cause  pain  in  the  glans  penis. 

Reflex  action  :  Certain  sensory  stimuli  are  received,  pass  up 
the  nerve-trunks  to  the  posterior  nerve-roots,  and  thus  to  the 
spinal  cord.  In  the  cord  the  impulse  may  be  sent  to  the  brain, 
producing  the  consciousness  of  pain,  etc.;  or  else  the  impulse 
in  the  cord  may  be  transmitted  directly  to  some  motor  cell  in 
the  anterior  horn,  stirring  it  to  activity,  with  the  result  that 
there  is  some  muscular  action.  For  example,  a  person  may 
be  tickled  with  a  feather  :  the  subject  brushes  away  the  offend- 
ing object  either  with  or  without  consciousness  of  what  he  is 
doing.  If  he  does  it  unconsciously,  the  reflex  act  takes  place 
in  the  cord ;  if  he  brushes  away  the  feather  as  a  result  of 
the  impression  received  in  his  brain,  the  reflex  act  took  place 
in  the  brain.  Furthermore,  a  person  may  perform  a  reflex 
act  through  the  reflex  centres  in  the  cord,  and  yet  after 
the  act  is  completed  he  may  receive  the  sensory  impulse 
in  the  brain.  From  this  we  may  deduce  the  following 
rule : 


182  NERVOUS  SYSTEM. 

A  reflex  act  taking  place  through  the  cord,  may  or  may  not 
be  accompanied  by  conscious  sensation  ;  but  if  it  is  accompa- 
nied by  conscious  sensation,  the  consciousness  is  always  later 
in  point  of  time  than  the  act.  Thus  we  may  say  a  reflex  ac- 
tion is  an  action  which  results  from  a  centripetal  nerve-im- 
pulse passing  to  a  nerve-centre  in  a  ganglion,  and  there  trans- 
forming to  a  centrifugal  impulse  passing  to  a  muscle.  Such 
an  action  may  be  simple  and  involve  a  single  muscle,  or  com- 
plex and  involve  many  :  thus,  a  ray  of  light  falling  upon  the 
retina  causes  a  simple  reflex  contraction  of  a  single  muscle, 
and  the  iris  contracts.  As  an  illustration  of  a  complex  reflex 
action,  however,  irritation  of  the  larynx  causes  not  only  a 
closing  of  the  glottis,  but  a  contraction  of  all  the  muscles  in- 
volved in  forced  expiration  or  coughing. 

Reflex  acts  are  more  noticeable  in  the  cerebro-spinal  sys- 
tem ;  but  they  may  belong  to  either,  or  may  be  mixed,  the 
impulse  going  by  the  one  system  and  returning  by  the  other. 
Examples:  sneezing,  coughing,  swallowing  are  cerebro-spinal 
reflexes  ;  the  vaso-motor  reflexes  are  largely  sympathetic,  but 
the  centripetal  nerve  is  often  cerebro-spinal,  as  in  the  secre- 
tion of  saliva  or  in  blushing. 

The  spinal  cord  in  man  is  so  much  under  the  control  of 
the  higher  centres  that  its  capabilities  for  reflex  action  nro 
often  overlooked.  After  injury  to  the  spinal  cord  the  reflex 
acts  are  apt  to  be  purposeless  and  fruitless.  In  many  lower 
animals  reflex  actions,  after  the  cord  has  been  divided,  are 
often  followed  by  extensive  and  coordinated  movements.  In 
the  frog  this  is  especially  marked.  Yet  the  difference  is 
one  of  degree  only.  In  man  many  minor  acts  are  per- 
formed as  reflex  movements  occurring  through  the  aid  of  the 
spinal  cord,  although  the  cord  is  incapable  of  initiating  them 
of  itself. 

Special  reflexes  of  the  cord :  Under  this  heading  we  may 
enumerate  the  micturition,  defecation,  and  genital  centres  : 

(1)  Micturition:  Here  the  sphincter  of  the  bladder  is  kept 
in  a  normal  state  of  contraction,  until  such  time  as  afferent 
impulses  are  sent  to  the  cord  from  the  neck  of  the  bladder 
owing  to  pressure  of  urine;  an  efferent  impulse  is  then 
aroused  which  releases  the  sphincter  and  at  the  same  time 


SPECIAL  REFLEXES  OP  THE  CORD. 


183 


FIG.  93. 


causes  the  wall  of  the  bladder  to  contract  (Fig.  93). 
though  this  act  is  a  reflex  one,  it  is 
under  the  control   of  the   will  to  a 
large  extent. 

(2)  Defecation :  The  nature  of  the 
act  is  identical  with  that  of  micturi- 
tion :    the   impulse  arising  from    the 
presence  of  flatus  or  faeces,  with  the  re- 
sultant relaxation  of  the  sphincter  ani 
and  contraction  of  the  lower  bowel. 

(3)  Genital:  Controls  the  erection  of 
the  penis  and  the  ejaculation  of  semen. 
Under  this  heading  we  may  also  in- 
clude    the    centre     for    parturition. 
Stimulation    of  the    interior    of   the 
uterus  by  its  contents  may  excite  the 
centre  enough  to  cause  it  to  send  out 
impulses   producing   uterine  contrac- 
tions and   expulsion   of  its  contents. 
That  delivery   can   take   place   in    a 
person  under  the  influence  of  chloro- 
form shows  that   the  centre  is  inde- 
pendent of  the  will.     As  in  the  case 
of  micturition  or  defecation,  there  is 
an  accessory  action  of  the  abdominal 
muscles,  for  the  most  part  reflex  and 
involuntary. 


Al- 


Schema  of  micturition.  AC, 
EC,  C,  automatic,  reflex, 
and  cerebral  centres;  B, 
bladder ;  S,  sensory  centre 
acted  on  by  afferent  im- 
pulses (Landois). 


All  these  reflexes  have  their  seat  in  the  lumbar  enlarge- 
ment of  the  cord. 

Varieties  of  reflex  acts :  Reflex  actions  may  be  simple  or 
coordinated,  primary  or  secondary.  In  the  simplest  reflex  act 
only  a  single  nerve-cell  with  an  afferent  and  an  efferent  fibre 
is  concerned.  In  most  reflexes,  however,  it  is  probable  that 
several  cells  are  involved  and  act  in  concert.  Primary  reflex 
acts  are  those  such  as  sucking,  which  the  infant  can  perform 
as  well  as  the  adult.  Secondary  or  acquired  reflexes  are 
those  which  require  an  effort  of  the  will  for  their  first  per- 
formance, but  which  become  habitual  after  frequent  repeti- 
tion. They  are  described  under  Coordination. 


184  NERVOUS  SYSTEM. 

Augmentation :  The  resultant  reflex  act  of  a  stimulation 
may  be  far  in  excess  of  the  amount  of  stimulation  received. 
For  example  :  a  tiny  drop  of  acetic  acid  applied  to  the  skin 
of  a  decapitated  frog  may  result  in  most  frantic  efforts  on  the 
part  of  the  animal  to  rub  off  the  offending  fluid,  although 
the  irritation  can  be  but  slight.  The  explanation  lies  in  the 
fact  that  the  sensory  nerve- fibres,  as  they  enter  the  cord,  in- 
dividually break  up  into  an  ascending  and  a  descending  limb. 
These  two  limbs  in  turn  give  out,  at  several  points  along 
their  course,  collaterals,  which  break  up  into  sets  of  brush- 
endings.  These  "  brush-endings  "  connect  with  the  demlrites 
of  motor  cells.  Thus  it  is  seen  that  one  sensory  fibre  may 
stir  into  activity  several  motor  fibres,  so  that  the  resultant  act 
is  augmented. 

Automatic  acts  :  In  normal  subjects  the  cord  is  not  tho  scat 
of  many  automatic  acts.  But  if  the  brain  be  destroyed  or 
severed  from  the  cord,  certain  centres  which  normally  are 
secondary  assume  primary  importance  and  are  capable  of  au- 
tomatic activity.  The  best  examples  are  the  vaso-motor 
centres  of  the  cord. 

Under  the  capitulation  of  normal  automatic  coifrcx  we 
may  include  those  governing  the  sweat  and  general  mus- 
cular tone. 

The  student  must  bear  in  mind  that  there  are  many  auto- 
matic acts  whose  centres  are  outside  of  the  cord,  their  origin 
being  in  local  centres.  Thus,  there  are  certain  actions  which 
continue,  and,  while  they  are  closely  related  to  reflex  action, 
do  not  seem  to  be  true  reflexes,  but  to  originate  in  the  part. 
Thus,  the  peristaltic  action  of  the  alimentary  tract  is  not  de- 
pendent upon  the  presence  of  food  in  the  intestines,  but  may 
be  excited  in  the  absence  of  food  or  checked  when  it  is  pres- 
ent. This  action  has  been  referred  to  small  ganglia  and 
nerve-plexuses  found  there  (Auerbaeh's  and  Meissner's),  and 
is  considered  to  originate  in  the  local  nerve-centres.  This  is 
what  is  known  as  automatism  or  automatic  nerve-action. 

Coordination:  The  coordination  of  the  cord  is  nothing  but 
a  repetition  of  ordinary  reflex  acts  for  our  daily  lives.  F<>r 
example,  we  look  upon  walking  as  a  coordinate  movement. 
It  is  performed  unconsciously  and  depends  on  reflex  activity 


GROSS  ANATOMY.  185 

resulting  from  cutaneous  and  muscular  sensations,  or  the 
sense  of  position  in  space. 

Inhibition  of  reflex  acts  :  This  function  does  not  originate  in 
the  cord,  but  in  the  brain  ;  but  the  transference  of  the  impulse 
takes  place  in  the  reflex  centres  of  the  cord.  It  is  the  ability  to 
control  or  modify  reflex  action  by  an  effort  of  the  will  or  by 
mental  action  which  is  not  consciously  voluntary.  As  an  ex- 
ample of  this,  if  the  palm  of  a  sleeping  child  be  touched  by  the 
finger,  the  baby's  hand  will  grasp  the  finger ;  but  if  the  child 
is  awake,  no  such  reflex  occurs  :  it  is  checked  by  mental 
action.  Again  :  one  may  avoid  crying  out  when  in  pain  by 
an  effort  of  the  will,  or  may  hold  the  feet  still  when  the  soles 
are  tickled.  An  example  of  this  inhibition  of  reflex  action 
is  offered  in  the  knee-jerk,  an  important  sympton  in  the  diag- 
nosis of  certain  nervous  diseases.  When  the  patellar  tendon 
is  tapped  sharply  with  the  tips  of  the  fingers  the  foot  and  leg 
are  suddenly  jerked  forward.  If  the  patient  is  ignorant  of 
what  is  to  be  done,  the  amount  of  motion  obtained  is  diag- 
nostic ;  but  if  he  knows  what  is  expected,  the  result  is  apt  to 
be  deceptive,  as  this  reflex  can  be  entirely  prevented  by  the 
will.  For  this  reason,  if  the  patient  knows  the  symptom,  it 
is  always  tried  when  he  is  off  his  guard. 

The  object  of  reflex  acts  is  to  save  time,  suffering,  and 
wear  and  tear  on  the  body  ;  but  if  we  had  no  check  on  reflex 
activities,  we  should  spend  all  our  time  making  efforts  to 
escape  outside  stimuli. 

Medulla  Oblongata. 

Gross  anatomy  :  The  medulla  oblongata,  or  bulb,  is  a  column 
of  white  and  gray  nerve-substance,  the  lowermost  portion  of 
the  brain,  and  connecting  with  the  spinal  cord  below. 

The  white  substance  is  composed  of  the  medullary  fibres 
continued  up  from  the  cord,  and  the  gray  matter  is  arranged 
variously  between  the  bands  of  white  fibres.  It  has  an  an- 
terior and  a  posterior  fissure,  corresponding  to  those  of  the 
cord,  and  the  central  canal  of  the  cord  here  opens  into  the 
fourth  ventricle. 

The  medulla  continues  in  a  general  way  the  arrangement 


186  NERVOUS  SYSTEM. 

of  the  fibres  in  tracts  of  the  cord  below ;  but  as  the  diameter 
is  greater,  the  general  shape  is  pyriform  and  the  shape  of  the 
columns  is  changed  (Fig.  94).  The  anterior  columns  of  the 
cord  correspond  in  position  to  the  pyramids  of  the  medulla ; 
the  posterior  columns,  to  the  restiform  bodies  ;  and  the  lateral 
columns  correspond  to  the  lateral  tract  of  the  medulla  with 
the  olivary  bodies.  The  fibres,  however,  do  not  follow  this 

FIG.  94. 


Middle 
peduncle  of 
cerebellum. 


Medulla  oblongata  and  pons  Varolii,  anterior  surface. 

arrangement  so  closely,  but  are  distributed  variously  in  the 
medulla. 

The  anterior  columns  of  the  cord  send  some  of  their  fibres 
(the  direct  pyramidal  tract)  into  the  pyramids,  forming  con- 
tinuous tracts.  Fibres  from  the  lateral  columns  also  enter 
the  pyramids,  but  cross  in  bundles  to  the  opposite  side.  These 
fibres  may  be  seen  crossing  the  anterior  fissure  between  the 
pyramids  by  gently  separating  them.  This  is  known  as  the 
decussation  of  the  pyramids.  The  fibres  which  cross  in  this 
way  belong  in  the  cord  to  the  portion  of  the  lateral  column 
known  as  the  crossed  or  lateral  pyramidal  tract. 


MEDULLA.  187 

Further  course  of  the  fibres  of  the  pyramids :  Almost  all  of 
the  fibres  pass  on  through  the  pons  Varolii  and  crusta  of  the 
mid-brain,  to  be  distributed  to  the  cortex  of  the  hemispheres 
by  way  of  the  internal  capsule  and  corona  radiata.  A  few 
of  the  fibres  (external  arciform)  pass  to  the  cerebellum  by 
way  of  the  restiform  body. 

Lateral  columns  :  The  lateral  column  of  the  cord  is  broken 
into  three  tracts  in  the  medulla  :  one,  we  have  just  seen,  joins 
the  anterior  pyramid  of  the  opposite  side  by  the  decussation  ; 
a  second  joins  the  restiform  body  on  its  way  to  distribution 
in  the  cerebellum  ;  while  the  third  set  of  fibres  passes  through 
the  deeper  part  of  the  medulla  (formatio  reticularis)  and 
tegmentum  of  the  mid-brain,  and  reaches  the  ganglia  at  the 
base  of  the  brain  ;  some  of  these  go  to  the  fillet. 

Posterior  columns :  The  fibres  of  the  posterior  column  con- 
tinue on  as  the  funiculi  cuneatus  and  gracilis  of  the  medulla. 
These  in  turn  terminate  in  their  own  nuclei,  from  which  new 
fibres  arise  and  pass  to  the  fillet  of  the  opposite  side.  The 
restiform  body,  just  above  the  ends  of  these  funiculi,  for  the 
most  part  reaches  the  cerebellum.1 

Olivary  bodies :  Each  is  a  mass  of  white  nerve-substance 
containing  a  central  gray  nucleus.  There  are  communications 
between  it  and  some  of  the  tracts  from  the  cord,  especially 
from  those  tracts  of  the  anterior  and  lateral  columns  which 
go  to  the  ganglia  at  the  base  of  the  brain. 

Medulla — arrangement  of  the  gray  matter:  As  the  fibres 
which  form  the  crossed  pyramidal  tract  pass  from  the  lateral 
column  to  decussate  into  the  pyramid  of  the  opposite  side, 
they  push  the  anterior  cornu  of  the  gray  matter  backward  ; 
and  this  is  still  further  accomplished  by  the  olivary  body, 
until  the  gray  matter  is  spread  out  toward  the  posterior  sur- 
face of  the  medulla  at  its  upper  part.  Here  the  central  canal 
of  the  cord  has  widened  out  to  form  the  lower  part  of  the 

1  In  speaking  of  these  fibres  it  has  been  convenient  to  say  that  they  "pass" 
in  certain  directions  or  " are  distributed"  in  some  situation.  It  must  not 
be  forgotten  that  they  are  afferent  and  efferent  medullated  nerve-fibres,  and 
that  such  terms  must  be  considered  as  somewhat  figurative.  In  reality,  it 
would  not  seem  proper  to  speak  of  an  efferent  fibre  as  being  "  distributed  " 
at  its  origin,  but  convenience  and  usage  permit  the  use  of  these  and  similar 
expressions. 


188  NERVOUS  SYSTEM. 

fourth  ventricle,  and  the  gray  substance  is  aggregated  just 
under  the  floor  of  the  ventricle.  There  are  also  sonic  other 
collections  of  gray  matter — for  example,  in  the  olivary  bodies. 

In  this  gray  substance  are  the  nuclei  of  origin  of  some  of 
the  cranial  nerves :  the  spinal  accessory,  hypoglossal,  pneu- 
mogastric,  and  glosso-pharyngeal  nerves  ;  and  roots  of  the 
auditory,  of  the  facial,  and  of  the  trigeminus  nerves,  arise  in 
this  important  collection  of  gray  matter.  Of  the  smaller  col- 
lections of  gray  substance,  probably  none  has  the  peculiar 
interest  which  the  floor  of  the  fourth  ventricle  possesses  for 
this  reason. 

Function  of  the  medulla :  The  functions  of  the  medulla  are 
practically  of  the  same  kind  as  those  possessed  by  the  spinal 
cord,  but  of  a  higher  degree.  They  are  as  follows  :  (a)  con- 
duction ;  (6)  reflex  action  ;  (c)  automatic  action  ;  (d)  inhibition. 

Conduction:  As  the  medulla  is  the  sole  connecting  link 
between  the  upper  parts  of  the  brain  and  the  cord,  it  neces- 
sarily contains  all  fibres  passing  between  these  limits.  Thus 
it  conducts  all  impulses  and  transmits  all  sensations. 

Reflex  action:  The  medulla  resembles  the  spinal  cord  in 
being  the  seat  of  reflex  acts;  the  only  difference  between 
them  being  in  the  fact  that  many  of  the  reflexes  performed 
by  the  former  are  of  much  greater  importance  to  life  than 
any  performed  by  the  latter.  Of  the  many  reflex  acts  arising 
from  the  medulla,  the  following  are  examples : 

(1)  That  part  of  digestion  which  is  performed  in  the  mouth 
is  dependent  upon  medullary  reflexes — mastication,  degluti- 
tion, and  the  secretion  of  saliva;  and,  probably,  the  secretion 
of  the   pancreatic  and  other  digestive  juices.     In  this  con- 
nection the  so-called  vomiting-centre  may  be  noted. 

(2)  The  respiratory  functions  are  so-called  automatic  func- 
tions of  the  medulla,  and  are  capable  of  being  sustained  by 
the  nerve-force  derived  from  the  medulla  alone.     The  centres 
for  coughing  and  sneezing  are  also  here.     The  pneumogastrie 
and  phrenic  nerves  convey  the  afferent  and  efferent  stimuli, 
though    there    may   be   communications    with    other  nerves 
whereby  sensory  stimuli  are  applied. 

(3)  "  Cardiac  depressor"  is  the  name  given  to  a  bundle  of 
nerve-fibres  running  from  the  heart  to  the  medulla,  which  i< 


SPECIAL  CENTRES.  189 

stimulated  when  the  heart  is  overworking  against  a  high  ten- 
sion in  the  bloodvessels.  The  result  of  the  stimulation  of 
this  "  cardiac  depressor  "  is  a  stimulus  to  the  vaso-motor  nerves 
which  results  in  a  dilatation  of  the  arterioles,  and  conse- 
quently the  tension  is  diminished  and  the  overwork  of  the 
heart  ceases.  This  reflex  act  takes  place  in  the  medulla. 

Automatic  action :  The  impulses  which  are  sent  out  to 
muscles  without  apparent  afferent  stimuli,  and  without  an 
effort  of  the  will,  are  called  automatic.  Such  rhythmic  im- 
pulses as  those  which  maintain  the  respiratory  function  be- 
long to  this  class.  It  is  not  to  be  doubted  that  such  actions 
are  reflex,  and  in  response  to  stimuli.  In  the  case  of  the 
lungs,  for  example,  the  presence  of  deoxygenated  blood  may 
serve  to  excite  an  afferent  impulse.  Nevertheless,  some 
authors  distinguish  between  automatism  and  reflex  action. 
This  automatic  action  cannot  be  considered  as  at  all  the  same 
as  an  action  of  the  brain  proper,  like  volition,  but  rather  as 
a  high  grade  of  reflex  action.  On  the  other  hand,  some 
authorities  claim  that  it  is  truly  automatic  in  some  of  its  acts, 
in  that  it  is  capable  of  direct  stimulation  by  the  condition 
of  the  blood  circulating  through  the  environment.  It  is 
bilateral,  and  probably  consists  of  both  an  inspiratory  and 
an  expiratory  part.  It  may  be  influenced  to  a  certain  extent 
by  voluntary  impulses. 

Inhibition:  This  is  the  control  or  inhibition  of  action 
through  the  nerves  which  are  distributed  from  this  region 
and  through  the  communications  with  other  centres  in  the 
cord.  Besides,  there  are  supposed  to  lie  in  the  medulla 
centres  which  maintain  the  nutrition  and  tone  of  the  muscles. 
These  are  known  as  control  and  tonic  centres. 

Special  centres :  In  addition  to  the  centres  already  given 
there  is  a  considerable  number  of  centres  in  the  medulla  which 
control  many  important  and  complicated  coordinated  muscular 
actions.  These  are  centres  of  reflex  action  for  the  most  part- 
that  is,  are  called  upon  to  act  in  response  to  stimuli  derived 
from  an  afferent  impulse  or  to  a  voluntary  effort. 

The  following  are  examples  : 

(1)  Regulation  of  the  heart's  action  is  found  here,  both  inhib- 
itory and  accelerator  centres  communicating  through  the  vagus. 


190  NERVOUS  SYSTh'M. 

(2)  Vaso-motor — regulation  of  the  unstriped  muscular  fibre 
of  the   arteries   is    al>o    accomplished    by  the    medulla.     A 
peculiar  vaso-motor  disturbance  is  brought  about  by  injury  of 
one  centre  of  the  medulla — namely,  the  interference  with  the 
glycogen-function  of  the  liver  and  the  appearance  of  sugar 
in  the  urine — the  diabetic  centre. 

(3)  Various  centres  which  have  to  do  with  the  regulation 
of  the  body-temperature.     The  vaso-motor  centres  we  have 
already    mentioned.      There   are   also   found   special   wc«t- 
centres ;   and,  furthermore,  a  control  of  the   special   sweat- 
centres  found  in  the  cord  is  here  maintained.    Upon  plausible 
theoretical  grounds  there  is  also  assumed  to  be  a  licut-iiiliibi- 
tory  centre,  by  which  the  heat-production  is  controlled  without 
reference  to  vaso-motor  conditions. 

(4)  Also  see  example  under  "  Reflex  action." 

Other  functions :  The  origin  of  the  roots  of  certain  of  the 
cranial  nerves  here  has  caused  the  special  senses  of  hearing 
and  of  taste  to  be  referred  to  this  region ;  and  the  connection 
with  the  sympathetic  system  through  the  cord  has  caused  the 
centre  for  the  dilatation  of  the  pupil  to  be  located  in  the 
medulla.  Phonation  is  also  dependent  upon  the  action  of 
nerves  arising  in  this  focus  of  gray  matter,  and  no  voluntary 
or  reflex  sound  can  be  produced  by  an  animal  in  which  the 
speech-centre  in  the  medulla  is  destroyed.  The  origin  here 
of  the  hypoglossal  and  pneumogastric  nerves,  involving  as 
they  do  the  movements  of  the  tongue  and  glottis,  controls 
both  the  acts  of  phonation  and  articulation. 

Demonstration  of  respiratory  functions  of  the  medulla  :  For 
this  purpose  we  select  an  active,  healthy  frog  :  If  the  spinal 
cord  be  removed  up  to  the  medulla,  the  respirations  continue, 
and  in  the  same  way  they  do  not  cease  if  the  hemispheres  be 
removed  without  disturbing  this  organ  ;  or,  if  both  cord  and 
hemispheres  be  removed  without  disturbing  the  medulla,  the 
movements  of  breathing  will  continue.  If  the  medulla  is 
injured  at  the  origin  of  the  pneumogastric  nerve,  however, 
the  movements  of  respiration  cease  and  the  animal  dies. 
The  same  occurs  when  a  similar  injury  happens  in  the  higher 
animals  and  in  man.  Death  occurs  instantaneously  in  this 
way  when  the  medulla  is  broken  near  the  axis  in  executions 


CEUEA    CEREBRL  191 

by  hanging — "  the  neck  is  broken  " — or  when  an  animal  is 
killed  by  "pithing"  in  laboratory  experiments. 

Glosso-labio-laryngeal  paralysis  :  It  may  be  of  interest  at 
this  point  to  observe  the  pathological  changes  that  occur  in 
the  medulla  in  producing  the  disease  known  as  glosso-labio- 
laryngeal  or  bulbar  paralysis :  It  is  a  progressive  degenera- 
tion of  the  gray  matter  of  the  medulla,  and  it  shows  itself 
first  in  a  paralysis  of  the  tongue,  which  renders  articulation 
of  certain  sounds  indistinct :  as  the  degeneration  progresses 
in  the  medulla  articulation  becomes  more  and  more  im- 
possible and  deglutition  is  affected.  The  disease  continues  to 
aifect  more  and  more  of  the  functions  dependent  upon  the 
medulla,  until  death  ensues  as  a  result  of  involvement  of  the 
cardiac  and  respiratory  centres  or  of  inability  to  take  food. 

Pons,  Crura  Cerebri,  and  Corpora  Quadrigemina. 

The  pons  Varolii  is  a  collection  of  nervous  tissue  lying 
immediately  above  the  medulla.  It  consists  of  white  fibres, 
with  areas  of  gray  matter  filling  in  the  intervals  between  the 
fasciculi  of  white  fibres.  The  white  fibres  connect  the  mid- 
brain  with  the  medulla,  and  also  pass  between  the  hemi- 
spheres of  the  cerebellum.  What  is  the  function  of  the  gray 
matter  is  little  known ;  but  some  of  it  is  directly  continuous 
with  that  of  the  medulla,  and,  like  it,  active  as  a  centre  of 
nervous  force.  In  the  pons  is  the  decussation  of  many  nerve- 
fibres,  among  which  are  some  of  the  fibres  of  the  facial  nerve 
arising  in  the  floor  of  the  fourth  ventricle. 

Paralysis  following  lesions  of  the  pons  :  The  so-called  crossed 
paralysis  may  follow  lesions  in  the  lower  portion  of  the  pons 
— that  is,  paralysis  of  sensation  and  motion,  more  or  less 
complete,  of  the  opposite  side  of  the  body,  with  paralysis  of 
the  facial  muscles  of  the  same  side  as  the  lesion. 

Crura  cerebri :  The  crura  are  formed  of  fibres  passing  from 
the  medulla  through  the  pons  Varolii,  to  the  hemispheres  of 
the  cerebrum.  They  divide  so  as  to  form  two  sets  of  fibres  : 
the  more  superficial  (crustse)  are  mostly  motor  or  efferent  fibres 
which  are  continuous  with  the  pyramidal  tracts  in  the  cord; 
while  the  deeper  (tegmentum)  layer  of  fibres  are  afferent  or 


192  NERVOUS  SYSTEM. 

sensory,  and  are  derived  largely  from  the  lateral  and  posterior 
tracts  of  the  cord.  Lying  between  these  bands  of  fibre.-  i-  a 
mass  of  gray  substance  (locus  nigcr)  whose  function  as  a 
nerve-centre  is  not  understood,  though  it  has  to  do  with 
coordination  of  the  muscles,  and  especially  with  regulation 
of  the  muscles  controlled  by  the  motor  oculi  nerve. 

Paralysis  following  lesions  in  the  crura :  This  is  paralysis 
of  the  opposite  side  of  the  body,  both  of  sensation  and  motion, 
and  of  a  degree  of  intensity  depending  upon  the  size  of  the 
lesion  ;  and,  besides  this,  paralysis  of  the  motor  oculi  nerve 
of  the  same  side  as  the  lesion.  There  is  a  derangement  of  the 
coordination  of  motions  which  follows  lesions  of  this  region 
beyond  that  which  belongs  to  the  motor  paralysis;  this  is 
often  shown  in  rotary  movements  when  the  subject  attempts 
to  walk.  It  is  inferred  that  there  are  coordinating  influences 
derived  from  the  crura. 

The  corpora  quadrigemina  are  four  rounded  eminences 
placed  in  pairs,  two  anterior,  two  posterior.  They  are  situ- 
ated on  the  dorsal  aspect  of  the  mid-brain  below  the  posterior 
lobes  of  the  cerebral  hemispheres  and  between  the  optic 
thalami  and  third  ventricle  in  front  and  the  cerebellum 
behind. 

Functions:  The  anterior  corpora  quadrigemina  are  the 
homologues  of  the  optic  lobes  in  some  of  the  lower  animals, 
and  the  anterior  pair  may  be  regarded  as  important  centres 
for  the  visual  and  motor  functions  of  the  eyes.  The  posterior 
pair  are  more  intimately  associated  with  the  sense  of  hearing. 
The  special  functions  of  the  corpora  quadrigemina  will  be 
more  fully  discussed  under  the  special  senses.  Not  only  doe- 
blindness  follow  lesions  of  the  anterior  corpora  quadrigemina, 
but  there  is  often  atrophy  of  them  when  the  eyes  are  de- 
stroyed.. 

Cerebrum. 

The  cerebrum  is  composed  of  two  hemispheres,  connected  by 
a  commissure  of  white  fibres,  the  corpus  callow  m,  and  of  the 
third  ventricle  and  optic  thalami  (di-  or  thalamencephalon). 

The  two  hemisphere*  are  separated  by  a  deep  fissure  ex- 
tending from  before  backward,  and  in  the  interior  of  each  is 


REGIONS  OF  THE  CEREBRUM.  193 

found  a  cavity  known  as  the  lateral  ventricle.  The  hemi- 
spheres are  connected  directly  with  the  spinal  system  by  the 
crura  cerebri  and  medulla,  and  with  each  other  by  the  corpus 
callosum.  They  are  composed  of  white  and  gray  nerve- 
substance,  and  the  latter  is  arranged  largely  at  the  periphery 
of  the  hemispheres ;  the  former  being  made  up  of  communi- 
cating nerve-fibres  which  connect  the  various  portions  of  the 
hemispheres  with  each  other,  and  the  hemispheres  with  other 
parts  of  the  cerebro-spinal  system,  thus  allowing  a  free 
control  of  the  impulses  arising  from  one  cell  or  set  of  cells 
by  other  cells  in  the  gray  matter. 

The  surface  of  the  cerebrum  is  divided  into  regions  by 
fissures,  which  separate  one  part  from  another.  These  fis- 
sures are  always  present,  and  upon  them  depends  the  deter- 
mination of  the  division  of  the  cerebrum  into  lobes.  Fissures 
which  are  of  use  in  locating  the  lobes  of  cerebral  matter  are 
the  fissure  of  Rolando,  the  fissure  of  Sylvius,  and  the  parieto- 
occipital  fissure  (Fig.  95). 

Convolutions :  The  surface  of  the  brain  is  further  cut  up  by 
a  number  of  other  clefts,  known  as  sulci  ;  and  these  separate 
the  surface  into  a  number  of  distinct  masses  or  convolutions. 
The  depth  of  the  sulci  and  their  number  determine  the 
quality  of  the  brain  in  respect  to  its  degree  of  development ; 
thus,  the  convolutions  in  man  are  much  deeper  and  more 
numerous  than  in  the  lower  animals.  The  sulci  are  not  in- 
variable in  position  or  number  in  different  brains. 

Regions  of  the  cerebrum:  (1)  Frontal  lobe:  This  lobe  is 
bounded  by  the  fissure  of  Rolando,  and  contains  several  con- 
volutions which  include  the  forward  portion  of  the  brain. 

(2)  The  parietal  lobe  lies  behind  the  fissure   of  Rolando, 
and  extends  posteriorly  to  the  occipito-parietal  fissure.     The 
convolutions  are  well  marked,  and  are  separated  by  a  well- 
marked  sulcus  (sometimes  known  as  the  intra-parietal  fissure) ; 
and  the  posterior  branch  of  the  fissure  of  Sylvi  us  is  enfolded 
by  an  inferior  parietal  convolution,  known  as  the  "  supramar- 
ginal  convolution." 

(3)  The  tempo  ro-sphenoidal,  or  temporal  lobe,  is  below  the 
Sylvian  fissure  and  in  front  of  the  occipital  lobe.     Its  convo- 
lutions are  well  marked. 

13— Phys. 


1(J4 


NERVOUS  SYSTEM. 


(4)  The  occipital  lobe  is  found  at  the  posterior  end  of  the 
cerebral  hemisphere,  and  its  convolutions  are  continuous  with 
those  of  the  parietal  and  temporo-sphenoidal  lobes,  except 
within  the  longitudinal  fissure,  where  it  is  cut  off  from  the 
parietal  by  the  parieto-occipital  fissure. 


Plan  of  the  human  brain  in  profile,  showing  its  fissures  and  convolutions.  S,  fissure 
of  Sylvius  ;  S',  anterior  branch ;  S",  posterior  branch ;  R,  fissure  of  Rolando  ;  P, 
intraparietal  fissure. 


(5)  The  central  lobe,  or  island  of  Rctt,  is  within  the  fissure 
of  Sylvius,  and  is  covered  by  convolutions  of  the  frontal  and 
parietal  and  temporal  lobes  (see  5  in  Fig.  96). 

Besides  these  well-defined  lobes,  the  portion  of  the  cerebral 
surface  which  is  trithin  fin-  longitudinal  fixture  is  marked  l>v 
sulci  and  convolutions.  Convolutions  of  the  frontal,  parietal, 
and  occipital  lobes  are  found  here:  the  marginal  convolu- 
tion, the  gyms  fornicatus  lying  above  the  corpus  eallosum, 
the  paracentral  lobule,  the  quadrate  lobule,  and  the  cuneato 
lobule  are  among  the  principal  landmarks. 


ARRANGEMENT  OF  THE  GRAY  MATTER.  195 

Arrangement  of  the  gray  matter :  The  increase  in  the  area 


Horizontal  section  of  the  hemispheres  at  the  level  of  the  cerebral  ganglia.  1, 
great  longitudinal  fissure  between  frontal  lobes  ;  2,  great  longitudinal  fissure 
between  occipital  lobes :  3,  anterior  part  of  corpus  callosum ;  4,  fissure  of 
Sylvius  ;  5,  convolutions  of  the  insula  ;  6,  caudate  nucleus  of  corpus  striatum  ; 
7,  lenticular  nucleus  of  corpus  striatum  ;  8,  optic  thalamus ;  9,  internal  capsule  ; 
10,  external  capsule ;  11,  claustrum. 

of  the  surface  of  the  hemispheres  by  the  infolding  of  the 
sulci  adds  very  greatly  to  the  amount  of  gray  substance  in 


196 


NERVOUS  SYSTEM. 


FIG.  97.    Gray  matter  of  the  cerebral 
cortex  (Muyiicrt). 


the  brain  ;  for  the  entire  sur- 
face i.s  composed  of  gray  sub- 
stance, and  this  follows  the 
sulci  and  fissures  (Fig.  96) 
in  all  their  folds,  and  is  not 
cut  into  by  them. 

Besides  the  gray  matter  in 
the  convolutions,  there  are 
certain  other  grav  masses  in 
the  substance  of  the  white 
matter;  the  optic  thalami, 
the  corpora  striata,  and  the 
claustrum  (Fig.  96)  are  the 
chief  of  these  gray  masses. 
Minute  structure  of  the  gray 
matter  :  The  gray  matter  of 
the  cortex  is  made  up  of  gan- 
glion-cells of  various  shapes 
and  sizes  lying  in  a  loose 
neuroglia-stroma,  more  abun- 
dant at  the  surface.  The 
cells  are  the  source  of  numer- 
ous nerve-fibres,  which  par-s 
out  into  the  white  matter 
(Fig.  97).  There  are  counted 
five  layers  of  these  ganglion  ie 
tissues;  and  while  these  zones 
merge  into  one  another,  they 
are  tolerably  distinct.  In 
the  middle  (and  widest)  Inver 
large  multi  polar  cells  are  very 
numerous,  and  the  fibres  may 
be  seen  to  pass  through  the 
deeper  layers  in  bundles  into 
the  white  matter. 

Chemistry  of  brain-tissue  : 
Brain-tissue  consists  of  some 
peculiar  bodies  allied  to  the 
rats,  but  containing  nitrogen  ; 


COURSE  OF  THE  FIBRES  IN  THE  HEMISPHERES.     197 

of  these,  cerebrin  and  lecithin  are  the  more  prominent.  Aside 
from  these,  the  constituents  are  proteid  and  fatty  substances, 
with  salts,  chiefly  potassium  and  magnesium  phosphates,  and 
water. 

Weight  of  brain :  About  three  pounds.  In  size  it  exceeds 
the  brains  of  all  the  lower  animals  except  those  of  the  ele- 
phant and  whale.  Its  weight  is  about  one-fortieth  of  the 
total  body-weight,  and  this  ratio  is  greater  than  in  the  lower 
animals,  with  a  few  exceptions  among  the  smaller  birds  and 
monkeys.  In  women  the  weight  is  about  one-tenth  less  than 
in  men. 

Relation  of  size  of  brain  to  the  intellect:  In  some  degree 
the  size  of  the  brain  bears  a  direct  relation  to  the  intellect  of 
the  individual,  but  this  is  not  absolute.  The  depth  of  the 
sulci  and  the  consequent  size  and  complexity  of  the  convolu- 
tions are  a  more  efficient  measure  of  the  brain-power.  In  the 
largest  of  the  apes  the  brain  of  an  adult  animal  is  about  the 
same  in  weight  as  that  of  a  human  infant  at  birth.  Idiots, 
as  a  rule,  have  brains  much  smaller  than  the  normal,  and  in 
them  the  convolutions  are  apt  to  be  ill-marked  and  uncom- 
plicated, as  is  the  case  in  the  lower  animals. 

Course  of  the  fibres  in  the  hemispheres  :  The  course  of  these 
fibres  may  be  classified  in  three  groups  :  1,  commissural  fibres; 
2,  fibres  of  association ;  and  3,  medullary  fibres. 

(1)  The  eommissural  fibres  are  those   which  connect  one 
hemisphere  with   the   other,  and  it  may  be  said  that  these 
fibres  connect  each  set  of  convolutions  with  the  corresponding 
set  of  the  opposite  side.     The  convolutions  of  the  portion  of 
the  brain  lying  above  the  fissure  of  Sylvius  communicate  by 
the  corpus  callosum. 

(2)  Fibres  of  association  are  those  fibres  which  connect  the 
convolutions  of  one  hemisphere.    These  fibres  pass  in  bundles 
just  beneath  the  cortical  gray  matter  of  the  convolutions,  and 
it  is  thought  that  most  of  the  important  convolutions  of  each 
hemisphere  intercommunicate  in  this  way. 

(3)  The  medullary  fibres  are  those  which  connect  the  cere- 
brum and  medulla,  and  are  regarded  as  indirect  and  direct, 
according  as  they  do  or  do  not  pass  to  the  gray  ganglia  at  the 
base  of  the  cerebrum.     In  considering  the  course  of  the  fibres 


198  NERVOUS  SYSTEM. 

from  the  medulla  through  the  crura  cerebri  it  was  noted  that 
the  motor  and  sensory  fibres  were  to  some  extent  separated. 
The  fibres  pass  from  the  crusta  to  the  internal  capsule,  and 
hence  the  "direct  fibres"  pass  to  the  cerebral  convolutions 
through  the  corona  radiata ;  while  the  "  indirect  fibres  "  from 
the  legmen  turn  pass  to  the  corpora  striata  and  optic  thalami, 
and  communicate  with  ganglion-cells  in  them. 

Function  of  the  corpora  striata  and  optic  thalami:  These 
"basal  ganglia,"  with  the  other  collections  of  gray  substance, 
seem  to  have  a  controlling  influence  upon  the  spinal  system. 
It  is  through  these  ganglia  that  all  voluntary  impulses,  ex- 
cept those  by  the  direct  medullary  fibres,  must  pass.  These 
basal  ganglia  communicate  through  the  corona  radiata  with 
the  convolutions  of  the  cortex,  and  it  is  probable  that  we 
may  regard  this  part  as  acting  as  a  middleman  to  elaborate 
and  coordinate  the  voluntary  impulses  of  the  cortex  and  to 
act  in  matters  not  requiring  the  intervention  of  the  higher 
endowments  of  the  mind.  This  status  of  these  ganglia  is 
quite  theoretical,  but  the  function  may  be  considered  as  a 
sort  having  the  properties  of  both  the  automatism  of  the  gray 
matter  of  the  medulla  and  cord  and  the  voluntary  function 
of  convolutions.  In  this  consideration,  however,  we  must 
not  undervalue  the  communication  with  the  cortex  which 
these  basic  ganglia  possess. 

Lesions  of  the  basic  ganglia :  So  far  as  has  been  observed, 
the  corpora  striata  may  be  involved  by  considerable  lesions 
without  causing  persistent  motor  or  sensory  disturbances, 
and  the  same  may  be  said  of  the  optic  thalami  ;  but  if  the 
lesion  encroaches  upon  the  white  matter  of  the  internal 
capsule,  or  crura  cerebri,  the  effect  is  to  cause  more  or  less 
paralysis,  depending  upon  the  severity  of  the  lesion  and  its 
position. 

Functions  of  the  cerebrum:  The  motor  and  sensory  func- 
tions which  have  been  seen  to  belong  to  other  nuclei  or  gray 
matter  are  centred  here,  but  infinitely  broadened,  for  the  cells 
in  the  convolutions  of  the  cerebrum  can  originate  the  eilcivnt 
and  perceive  the  afferent  nerve-impulses.  In  fact,  it  is  iu 
this  portion  of  the  brain  that  the  intelligence  is  centred  :  it 
is  the  organ  of  the  mind.  Memory,  reason,  emotions,  and  all 


SENSORY  AREAS.  199 

the  other  attributes  of  the  mind  are  dependent  upon  its  func- 
tional power. 

Unilateral  action  of  the  brain  :  There  are  instances  in  which 
injury  or  disease  of  one-half  of  the  cerebrum  has  left  the 
intellectual  faculties  not  gravely  impaired.  From  a  consider- 
ation of  such  cases  it  has  been  held  that  the  action  of  one  of 
the  hemispheres  is  sufficient  for  the  purposes  of  the  mind. 
There  is,  however,  an  absolute  dependence  for  motor  and 
sensory  functions  upon  the  integrity  of  both  sides,  for  the  one 
side  cannot  act  for  the  other  in  these  functions.  As  a  rule, 
it  is  safe  to  assume  that  the  hemispheres  act  in  unison. 

Localization  of  brain-function :  While  the  brain  is  regarded 
as  an  organ  of  the  mind,  it  is  probable  that  the  various  func- 
tions may  be  regarded  as  belonging  to  definite  portions  of  the 
convolutions  which  are  appropriated  for  that  purpose.  The 
functions  of  the  convolutions  have  not  been  assigned,  except 
for  a  small  portion  of  the  brain-surface  and  for  some  of  the 
simpler  actions.  For  the  most  part,  our  knowledge  of  the 
exact  localization  of  brain-functions  is  confined  to  "motor 
areas,"  in  which  it  has  been  determined  that  stimulation  of  a 
certain  group  of  cells  will  cause  a  definite  action.  Besides 
this,  certain  other  centres  are  located,  as  of  sight  and  speech. 

Determination  of  motor  areas:  When  the  surface  of  the 
brain  is  exposed  in  animals  or  in  man,  the  stimulation  of 
certain  areas  of  the  cortex  by  a  mild  electrical  current  will 
give  rise  to  motion  in  the  peripheral  muscles  ;  and  it  is  found 
that  the  stimulation  of  the  same  region  in  the  same  or  other 
animals  will  cause  the  same  results.  These  centres  of  motor 
impulses  are  situated  almost  entirely  upon  the  convolutions 
about  the  fissure  of  Rolando  (Fig.  98). 

Sensory  areas:  These  have  not  been,  by  any  means,  so 
definitely  fixed  as  the  motor  centres ;  but  the  centres  for  sen- 
sation may  be  said  to  exist,  and  probably  in  the  convolutions 
of  the  posterior  portion  of  the  cerebrum.  The  centre  for 
vision  in  the  convolutions  about  the  posterior  branch  of  the 
fissure  of  Sylvius  is  generally  accepted ;  or  in  the  cuneate 
lobule  (14,  15,  in  Fig.  98).  The  centre  for  hearing  is  toler- 
ably defined  in  the  temporo-sphenoidal  lobe  along  the  pos- 
terior branch  of  this  fissure  (16,  Fig.  98).  The  speecA-centre 


200 


NERVOUS  SYSTEM. 


is  also  located  with  seeming  accuracy  along  the  anterior 
branch  of  the  fissure  of  Sylvius  and  in  the  third  frontal  convo- 
lution. This  centre  seems  to  be  much  more  developed  upon 
the  left  side  of  the  brain.  In  Fig.  98  this  centre  may  be 
indicated  roughly  by  reference  to  the  tongue-centres  (8  and  (h. 

FIG.  98. 


10 


Brain  of  monkey,  showing  the  position  of  the  motor  and  sensory  centres  as  ascer- 
tained by  Ferrier.  The  actions  all  occur  on  the  side  of  the  body  opposite  to  the 
part  of  the  brain  irritated.  1,  the  eyes  open  widely,  the  pupils  dilate,  and  head 
and  eyes  turn  toward  opposite  side  ;  2,  extension  "forward  of  the  opposite  arm 
and  hand,  as  if  to  reach  something  in  front;  3,  movements  of  tail  (and  trunk) : 
4,  retraction  with  adduction  of  opposite  arm;  5,  supination  and  llexioii  of  the 
forearm,  by  which  the  arm  is  raised  toward  the  mouth  ;  0,  action  of  zygomatics, 
by  which  the  angle  of  mouth  is  retracted  and  elevated;  7,  elevation  of  ala  of 
nose  and  upper  lip;  8,  opening  of  mouth  with  protrusion  of  tongue:  9.  retrac- 
tion of  tongue  ;  10,  retraction  of  opposite  angle  of  mouth  ;  a,  f>,  <\  <l,  prehensile 
movements;  11,  retraction  and  adduction  of  opposite  arm;  VJ.  advance  of  tin- 
opposite  hind  limb;  13,  complex  movements  of  thigh,  leg,  and  foot;  14, 16,  vision 
(sensory) ;  16,  hearing  (sensory). 

Pathological  support  of  localization :  Injuries  and  diseases 
involving  the  motor  areas  are  followed  by  paralysis  so  well 
defined  that  it  Is  frequently  possible  to  locate  the  seat  of  the 
lesion  from  its  result  upon  the  muscular  system.  Tumors. 
abscesses,  and  depressed  bone,  for  example,  are  capable  of 
accurate  localization  in  this  way.  The  more  indefinite  sen- 
sory paralyses  do  not  so  accurately  point  out  their  origin.  On 
;he  evidence  of  pathology  bears  out  in  full  the 
experimental  irttemlts.  The  crossed  action  of  all  the  nervous 


LI  BRARY 


ARRANGEMENT  OF  THE  GRAY  MATTER.  201 

structures  is  especially  to  be  noted.  In  the  case  of  a  right 
paralysis  in  which  the  speech  is  affected,  as  compared  with  a 
left  hemiplegia  and  speech  unaffected,  this  crossed  action  is 
impressed  when  we  remember  the  localization  of  the  centre 
for  speech  in  the  left  hemisphere  near  the  motor  area. 

Terms  used  in  defining  paralysis  :  Anaesthesia  =  loss  of  sen- 
sation. 

Hemiansesthesia  =  loss  of  sensation  in  one  lateral  half  of 
the  body. 

Hemiplegia  =  loss  of  muscular  power  in  one  lateral  half  of 
the  body. 

Paraplegia  =  symmetrical  loss  of  muscular  power  in  the 
lower  portion  of  the  body  and  extremities. 

Aphasia  =  loss  of  power  to  talk  :  amnesic  when  words  are 
forgotten  ;  ataxic  when  the  power  to  articulate  is  lost,  though 
the  words  are  known. 

The  Cerebellum. 

The  cerebellum  is  a  mass  of  nerve-substance  situated  pos- 
teriorly at  the  base  of  the  skull.  It  consists  of  a  median 
lobe  and  two  lateral  hemispheres,  and  is  connected  with  the 
rest  of  the  cerebro-spinal  system  by  numerous  white  fibres 
collected  in  bundles  known  as  peduncles.  Of  these,  the  larger 
peduncles  pass  to  and  largely  make  up  the  pons  Varolii 
(middle  peduncles),  thus  connecting  the  lateral  hemispheres 
of  the  cerebellum.  The  superior  peduncles  pass  beneath  the 
corpora  quadrigemina,  and  the  fibres  pass  into  the  cerebrum, 
decussating  as  they  meet  beneath  the  corpora  quadrigemina. 
The  inferior  peduncles  pass  to  the  medulla,  where  they  form 
the  restiform  bodies.  Thus  it  is  seen  that  the  entire  cerebro- 
spinal  system  communicates  very  freely  with  the  cerebellum. 

Arrangement  of  the  gray  matter :  The  arrangement  in  con- 
volutions is  not  the  same  as  in  the  cerebrum,  but  there  are 
numerous  transverse  sulci  which  divide  and  subdivide,  the 
gray  matter  being  disposed  about  them  in  a  thin  layer.  This 
causes  a  section  of  the  organ  to  have  a  peculiar  tree-like 
appearance,  which  originates  the  name,  "  arbor  vitse,"  given 
to  these  sections  of  the  cerebellum.  Besides  this,  there  is  a 

ntral  collection  of  gray  substance — the  corpus  dentatum. 


central  coll( 


202 


NERVOUS  SYSTEM. 
FIG.  99. 


External  gray  or 
cellular  layer. 


Corpuscles  of  Pnrkinje. 


Internal  or  rust- 
colored  layer. 


—  White  substance. 


Vertical  section  through  the  gray  matter  of  the  human  cerebellum  im 

about  100  diameters  :  Klein  and  Noble  Smith).    Two  branched  capillaries  are 
seen  at  the  upper  part  passing  into  the  gray  matter  from  the  pia  mater. 

Microscopic  examination  of  gray  matter :  Under  the  micro- 
scope it  is  found  to  consist  of  throe  layers  (Fig.  99).     The 


MOTOR   TRACT.  203 

outer  is  a  layer  of  delicate  "  connective  tissue  "  which  supports 
fine  nerve-fibres  and  small  spindle-shaped,  branching  nerve- 
cells.  The  middle  layer  is  characterized  by  irregularly  dis- 
posed large  ganglion-cells,,  and  the  branching  processes  from 
these  ramify  in  the  superficial  layer.  These  cells  are  known  as 
Purkinjrfs  cells.  The  inner  layer  is  made  up  of  a  mass  of  small 
spheroidal  cells,  and  gradually  merges  into  the  white  substance. 
Function  of  the  cerebellum  :  The  cerebellum  seems  to  exert 
no  influence  upon  the  sensory  nerves,  for  sensibility  is  not 
affected  by  its  injury  or  disease.  The  motor  system  is,  how- 
ever, entirely  disorganized  by  lesions  of  the  organ.  Coor- 
dination of  the  voluntary  muscles  is  accomplished  by  this 
portion  of  the  brain,  and  it  is  originated  in  the  gray  matter 
of  the  part.  It  has  no  effect  upon  the  senses  nor  upon  the 
intellect,  so  far  as  is  known. 

Tracts  in  Brain  and  Cord. 

The  motor  tract  consists  of  bundles  of  medullated  nerve- 
fibres  originating  in  cells  of  the  motor  area  of  the  brain. 
These  fibres  pass  downward,  between  the  optic  thai  am  us  and 
caudate  nucleus  on  the  inner  side  and  the  lenticular  nucleus 
on  the  outer  side.  During  this  part  of  their  course  the  fibres 
form  the  internal  capsule. 

Passing  down  in  the  crustce,  the  fibres  reach  the  pons. 
Here  the  fibres  change  position,  so  that  the  facial  fibres  cross 
over  from  the  inner  side  of  one-half  the  motor  tract  so  as  to  lie 
in  the  inner  half  of  the  opposite  motor  tract.  The  leg-  and 
arm-fibres  continue  down  in  their  respective  positions  without 
decussating  among  the  ventral  longitudinal  fibres  of  the  pons. 

On  leaving  the  pons  the  face-fibres  pass  out  through  the 
respective  cranial  nerves  to  the  muscles  of  the  face. 

The  leg-  and  arm-fibres  enter  the  medulla  and  decussate  to 
the  opposite  side  as  the  crossed  pyramidal  tract,  and  run  down 
as  the  "crossed"  column  of  the  cord  (the  lateral).  A  few 
fibres  continue  without  decussating,  in  the  anterior  column 
(column  of  Tiirck),  and  are  known  as  the  direct  pyramidal  tract. 
Thence  the  motor  fibres  pass  to  various  levels  of  the  cord. 

Lesions  of  the  motor  tract :  From  the  definite  anatomical 
course  of  the  motor  tract  we  may  conclude  that  definite  lesions 


204  NERVOUS  SYSTEM. 

at  any  point  of  its  course  will  give  definite  results.  Such  is  the 
case.  Naturally  a  lesion  of  the  motor  tract  gives  paralysis  as  a 
marked  symptom.  The  particular  nerves  and  the  n  tun  her  in- 
volved assist  us  in  locating  the  exact  area  of  the  tract  affected. 

1.  Lesions  on  the  cortex  or  in  the  internal  capsule  result  in 
a  variable  amount  of  paralysis ;  but  the  paralysis  is  on  the 
opposite  side  from  the  lesion. 

2.  Lesions  at  the  upper  border  of  the  pons  result  in  paralysis 
of  the  face  on  the  same  side  of  the  body,  but  of  the  arm  and 
leg  on  the  opposite  side  from  the  lesion. 

3.  Lesions  below  the  decussation  of  the  faee-fibrea  and  above 
that  of  the  arm  and  leg  leave  the  face  unaffected,  but  paraly/e 
the  arm  and  leg  of  the  opposite  side  of  the  body. 

Sensory  tract :  Starting  with  the  posterior  columns  of  the 
cord  (columns  of  Goll  and  Burdach),  the  sensory  fibres  pass 
into  the  medulla  as  the  funiculi  graciles  and  cuneati.  Here 
they  decussate  (decussation  of  the  fillet)  posterior  to  the 
median  raphe.  In  the  pons  they  form  the  straight  fillet, 
ascending  in  the  crura  cerebri  dorsal ly  to  the  motor  fibres 
(tegmentum).  As  part  of  the  corona  radiata,  sensory  fibres 
,are  then  distributed  to  that  portion  of  the  cerebral  cortex 
situated  well  behind  the  fissure  of  Rolando — /.  <-.,  posterior 
parts  of  the  parietal  and  occipital  lobes.  Their  terminations 
are  end-arborizations  with  sensory  cells. 

Mutilations. 

Mutilation  of  brain :  Numerous  experiments  have  been  con- 
ducted upon  animals  showing  the  effect  produced  on  the 
animal  of  the  removal  of  different  parts  of  the  brain.  Thus 
we  have  learned  by  deduction  the  functions  of  ninny  parts 
of  the  cerebro-spinal  system.  One  of  the  simplest  experi- 
ments, and  one  also  frequently  observed  in  surgery,  is  a 
division  of  the  spinal  cord. 

Division  of  the  spinal  cord:  The  result  is  a  complete  loss 
of  conductivity  between  the  two  segments  of  the  cord,  above 
and  below  the  point  of  division.  The  manifestation  is  a  loss 
of  sensation,  and  paralysis  of  the  parts  supplied  by  nerves 
emerging  from  the  cord  at  a  point  below  the  section.  Only 
such  reflexes  are  present  in  the  affected  parts  as  have  their 


REMOVAL   OF  THE  CEREBELLUM.  205 

seats  in  that  portion  of  the  cord  (below  the  section)  still  in 
connection  with  the  affected  areas.  The  parts  still  in  con- 
nection with  the  brain  (above  the  section)  retain  their  normal 
function.  If  the  section  be  made  between  the  medulla  and  the 
point  of  origin  of  the  phrenic  nerves,  death  from  asphyxia 
results. 

In  a  frog,  whose  spinal  cord  has  been  cut  close  to  the 
medulla,  and  whose  medulla  has  been  destroyed,  the  follow- 
ing results  are  noticed :  although  the  frog  does  not  respire 
through  his  lungs,  he  still  lives,  as  he  absorbs  oxygen  through 
the  skin,  provided  it  be  kept  moist.  The  animal  lies  prone 
on  its  belly.  If  dropped  into  a  basin  of  water,  it  sinks,  mak- 
ing no  attempt  to  swim ;  nor  does  it  swallow  food,  even  if 
placed  on  the  tongue. 

If  the  section  be  made  anterior  (above)  to  the  medulla,  the 
frog  breathes,  sits  in  a  normal  position,  swims  in  a  basin  of  water 
until  it  strikes  a  suitable  landing,  then  crawls  out  and  sits 
still.  It  makes  no  motion  unless  irritated,  then  hops  away  ; 
and  swallows  food  placed  on  the  tongue. 

Removal  of  the  cerebellum:  When  small  portions  are  re- 
moved the  animals  become  feeble  and  uncertain  in  "their 
movements,  but  are  able  to  move  for  ordinary  purposes.  As 
the  amount  removed  increases  the  want  of  coordination  of 
the  voluntary  muscles  increases.  With  the  entire  cerebellum 
gone  the  condition  is  absolute — animals  cannot  stand  nor  walk, 
nor  bring  any  of  the  muscles  into  orderly  action.  If  the 
animal  is  laid  upon  the  back,  it  cannot  recover  itself,  but 
struggles  vaguely  in  the  attempt.  The  senses  are  apparently 
normal  and  the  will-power  is  present :  if  a  blow  is  threatened, 
an  attempt  is  made  to  avoid  it.  When  the  lesion  is  confined 
to  one  hemisphere,  the  lack  of  coordination  is  noticed  in  the 
opposite  half  of  the  body.  Under  these  circumstances  the 
animals  are  apt  to  fall  to  the  opposite  side  and  roll  over  and 
over  rapidly.  Such  movements  are  known  as  forced  move- 
ments. This  condition  may  persist  for  several  days.  Pigeons 
from  which  the  cerebellum  is  removed  may  live  for  a  con- 
siderable time,  sometimes  for  several  months,  after  the  opera- 
tion. In  some  cases  there  is  a  return  of  power  to  coordinate, 
after  partial  removal,  at  the  end  of  some  days. 


206  NERVOUS  SYSTEM. 

Removal  of  the  cerebral  hemispheres  :  In  some  of  the  lower 
animals  the  cerebrum  may  be  entirely  removed  without  kill- 
ing them.  When  this  is  done,  for  example,  in  the  case  of  a 
pigeon,  the  bird  remains  quiet  in  one  position,  and  is  not  dis- 
turbed by  noises ;  or  if  thrown  from  its  perch,  it  Hies  and 
alights  in  a  nearly  normal  manner.  If  a  foot  be  pinched,  it 
withdraws  it  and  perhaps  changes  its  position.  The  bird  is 
capable  of  reflex  actions  of  various  complicated  kinds,  but 
there  is  no  spontaneous  exercise  of  volition  :  all  its  move- 
ments are  excited  by  the  nerve-stimuli  of  the  moment.  There 
is  no  perception  of  stimuli ;  the  intelligence  is  gone. 

Cranial  Nerves. 

The  cranial  nerves  are  a  set  of  twelve  pairs  of  nerves  which 
arise  from  the  brain.  They  are  varied  in  their  functions,  but 
all  arise  from  ganglia  of  the  gray  matter  in  the  brain  and 
medulla.  The  floor  of  the  fourth  ventricle  is  particularly 
rich  in  nuclei  in  which  these  cranial  nerves  originate. 

Classification  of  the  cranial  nerves:  In  the  order  of  their 
emergence,  by  numbers :  (I)  olfactory ;  (II)  optic ;  (III) 
motor  oculi ;  (IV)  patheticus  ;  (V)  trigeminus  ;  (Y  I)  alxlu- 
cens;  (VII)  facial;  (VIII)  auditory ;  (IX)  glosso-pharyn- 
geal ;  (X)  pueumogastric ;  (XI)  spinal  accessory  ;  ( X  1 1 )  hy- 
poglossal.  In  the  relation  of  their  functions  they  may  be 
arranged  as  nerves  of  special  sense,  nerves  of  common  sen>a- 
tion,  motor  nerves,  and  mixed  nerves  (/.  e.,  sensorv  and  motor). 

C  (I)  olfactory,  (II)  optic,  (VIII) 

XT  f         .  ,  auditorv  and  parts  of  the  (Y) 

Nerves  of  special  sense,  <  *  i    /Tv\ 

]       trigeminus    and    (IX)    glasso- 

^      pharyngeal. 

Nerves  of  common  sen-    f  The   greater  portion  of  the  (V) 
sation,  \       trigeminus. 

"  (III)  motor  oculi,(IV)  pathcticus, 
(V)  lesser  division    of  the   tri- 


Motor  nerves, 


geminus,  (  V  [)abducens,  (  V 1 1 ) 


facial,   and   (XII)  hypoglossal, 
(XI)  spinal  accessory  (?). 

(  (IX)  crlosso-pharyngeal  and  (X) 
Mixed  nerves, 

|       pneumogastrio. 


777  NERVE. 


207 


FIG.  100. 


Of  the  nerves  of  special  sense,  (I)  olfactory,  (II)  optic, 
and  (VIII)  auditory  will  be 
explained   later,  and   may  be 
omitted  from  further  consider- 
ation for  the  present. 

Ill  nerve :  It  arises  from  a 
nucleus  of  gray  matter  just  in 
front  of  the  pons  beneath  the 
iter  e  tertio  ad  quartum  ven- 
triculum  (aqueduct  of  Sylvius), 
passing  out  through  the  cms 
cerebri,  and  emerging  from  the 
skull  in  the  orbit  (Fig.  100). 
It  gives  off  some  fibres  to  the 
lenticular  ganglion.  It  is  dis- 
tributed to  all  the  muscles  of 
the  eyeball,  with  the  exception 
of  the  superior  oblique  and 
the  external  rectus  muscles. 
It  also  supplies  the  levator 
palpebrse  superioris  muscle, 
and  by  its  connection  with 
the  lenticular  ganglion  con- 
trols the  ciliary  and  pupillary 
muscles. 

It  is  purely  a  motor  nerve, 
function  is  best  described 
by  showing  the  paralyses  which 
"low  its  division  :  by  paraly- 

of  the  elevator  of  the  up- 
lid  we  have  ptosis;  by 
paralysis  of  the  muscles  of  the 
eyeball  we  have  inability  to 
move  the  organ  up  or  down 
or  inward  ;  by  the  unopposed 
action  of  the  external  rectus 
the  eyeball  becomes  turned 

outward  (external  strabismus) ;  by  paralysis  of  the  muscle  of 
the  iris  the  pupil  remains  dilated  and  does  not  respond  to 


A  partly  diagrammatic  view  of  the 
floor  of  the  aqueduct,  looking  upward 
(dorsally),  nuclei  of  the  third  and 
fourth  nerves,  and  the  decussating 
fibres  of  the  latter  all  shown;  the 
third  nerve  nuclei  are  subdivided 
into  an  anterior  nucleus,  the  Edinger- 
Westphal  nucleus  (a  and  6),  and  a 
posterior  nucleus ;  the  posterior  nu- 
cleus has  a  dorsal,  a  ventral,  and  a 
mesal  portion;  the  decussation  of 
the  fibres  from  the  dorsal  portion  of 
the  posterior  nucleus  of  the  third 
nerve  is  shown  (Edingerj. 


208  NERVOUS  SYSTEM. 

light ;  and  by  paralysis  of  the  ciliary  muscle  the  accommo- 
dation of  the  lens  for  near  vision  is  prevented. 

The  control  of  the  pupil  is  not  a  voluntary  one;  but  the 
effect  of  a  strong  voluntary  effort,  exerted  through  the  third 
nerve,  shows  itself  in  contraction  of  the  pupil,  as  when  the 
eyeball  is  turned  strongly  inward  and  upward. 

IV  nerve :  It  arises  close  by  the  third  nerve  beneath   the 
aqueduct  of  Sylvius,  and  emerges,  after  decussation,  from  the 
valve  of  Yieussens.     Thence,  passing  around  the  crus  cere- 
bri,  it  runs  parallel  with  the  motor  oculi  (third)  nerve  to  the 
orbit,  where  it  is  supplied   to  the  superior  oblique  muscle. 
Its  paralysis  prevents  the  muscle  from  maintaining  the  hori- 
zontal plane  of  the  eyeball.     If  this  paralysis  occurs,  there 
is  double  vision,  and  the  image  seen  by  the  affected  eye  ap- 
pears  oblique  and  inferior  to  the  image  of  the  other  eye.     This 
may  be  corrected  by  inclining  the  head  to  the  opposite  side. 
This  nerve  is  also  known  as  the  trochlearis  or  trochlear  nerve. 

V  nerve :  This  nerve  resembles  the  spinal  nerves  in  having 
a  motor  and  a  sensory  root,  the  latter  possessing  a  ganglion 
(Gasserian).     The  origin  of  the  nerve  seems  to  be  in  centres, 
separate  for  motor  and  sensory,  in  the  floor  of  the  fourth  ven- 
tricle (Fig.  101).     There  are  fibres  which  join  the  trunk  of 
the  nerve  which  are  derived  from  the  spinal  cord.     It  emerges 
from    the    pons  Varolii   as   two   distinct   nerve-roots.     The 
larger  of  the  two,  the    sensory,  soon    enters    the  Gasserian 
ganglion,  the  motor  root  passing  beneath  without  communica- 
tion.    The  nerve  then  breaks  up  into  three  branches:    of 
these  the  first  and  second  are  formed  entirely  from  the  sen- 
sory root,  while  the  third  carries  all  the  motor  fibres,  and  with 
them  some  of  the  sensory,  so  that  the  third  branch  of  the 
nerve  is  partly  sensory  and  partly  motor.     There  is  a  partial 
decussation- of  the  fibres  in  the  medulla,  but  many  pass  direct 
to  the  same  side. 

Muscles  supplied  by  the  motor  root,  V  nerve :  The  muscles 
supplied  are  those  of  mastication.  The  temporal,  ma>-< •!< T, 
and  both  pterygoid  muscles,  as  well  as  the  anterior  belly  of 
the  digastric  muscle  and  the  mylo-hyoid,  receive  their  inuer- 
vatiou  from  the  motor  root  of  the  fifth  nerve.  Besides  this, 
the  tensor  palati  and  tensor  tympnni  muscles  are  supplied 


SENSORY  FIBRES. 


209 


by  this  nerve  through  its  communication  with  the  otic  gan- 
glion of  the  sympathetic  system.     A  branch  to  the  buccinator 


View  of  the  posterior  surface  of  the  medulla,  the  roof  of  the  fourth  ventricle  being 
removed  to  show  the  rhomboid  sinus  clearly.  The  left  half  of  the  figure  repre- 
sents :  On,  funiculus  cuneatus  and,  (j,  funiculus  gracilis  ;  0,  obex;  sp,  nucleus 
of  the  spinal  accessory  ;  p,  nucleus  of  the  pneumogastric ;  p  +  up,  ala  cinera ;  R, 
restiform  body;  XII',  nucleus  of  the  hypoglossal;  t,  funiculus  teres  ;  a,  nucleus 
of  the  acusticus;  m,  strife  medullares';  1,  2,  and  3,  middle,  superior,  and  infe- 
rior cerebellar  peduncles  respectively ;  /,  fovea  anterior;  4,  eminentiateres  (genu 
nervi  facialis) ;  5,  locus  eceruleus.  The  right  half  of  the  figure  represents  the 
nerve-nuclei  diagrammatically  :  V,  motor  trigeminal  nucleus;  V,  median  and, 
V",  inferior  sensory  trigeminal  nuclei;  VI.  nucleus  of  abducens;  VII,  facial 
nucleus;  VIII,  posterior  median  acoustic  nucleus;  VIIF,  anterior  median; 
VIII",  posterior  lateral:  VIII'",  anterior  lateral  acoustic  nuclei;  IX,  glosso- 
pharyngeal  nucleus ;  A',  XI.  and  XII,  nuclei  of  vagus,  spinal  accessory,  and 
hypoglossal  nerves  respectively.  The  Roman  numerals  at  the  side  of  the  figure, 
from  'T  to  XII,  represent  the  corresponding  nerve-roots  (Erb). 

muscle  is  probably  not  motor,  but  sensory.     Lesions  of  the 
nerves  paralyze  these  muscles. 

The  sensory  fibres  of  the  fifth  nerve  are  distributed  in  all 
three  branches,  and  supply  sensation  to  the  skin  of  the  face 


210 


NERVOUS  SYSTEM. 


and  anterior  portion  of  the  head,  emerging  from  the  bony 
canals  upon  the  face  at  the  supraorbital,  infraorbital,  and 
mental  foramina.  Sensory  fibres  are  also  supplied  to  the 
mucous  membrane  of  the  mouth  and  tongue  (by  the  lingual 
branch)  and  to  the  muscles  of  the  part  (Fig.  102). 


FIG.  102. 


Diagram  of  the  fifth  nerve  and  its  distribution.  1,  sensitive  root;  2,  motor  root;  3, 
Gasserian  ganglion:  I,  ophthalmic  division;  II,  superior  maxillary  division; 
III,  inferior  maxillary  division  ;  4,  supraorbilal  nerve,  distributed  to  the  skin 
of  the  forehead,  inner  angle  of  the  eye,  and  root  of  the  nose;  5,  infra-orbital 
nerve,  to  the  skin  of  the  lower  eyelid,  side  of  the  nose,  and  skin  and  mucous 
membrane  of  the  upper  lip;  6,  mental  nerve,  to  the  integument  of  the  chin  and 
edge  of  the  lower  jaw,  and  skin  and  mucous  membrane  of  the  lower  lip  ;  »,  //, 


external  terminations  of  the  nasal  branch  of  the  ophthalmic  division,  to  the 
mucous  membrane  of  the  inner  part  of  the  eye  and  the  nasal  passages,  and  to 
the  base,  tip,  and  wing  of  the  nose  ;  t,  temporal  branch  of  the  superior  maxillary 


division,  to  the  skin  of  the  temporal  region  ;  m,  malar  branch  of  the  superior 
maxillary  division,  to  the  skin  of  the  cheek  and  neighboring  parts:  !>,  bucral 
branch  of  the  inferior  maxillary  division,  passing  along  the  surface  of  the  buc- 
cinator muscle,  and  distributee!  to  the  mucous  membrane  of  the  cheek  and  to 
the  mucous  membrane  and  skin  of  the  lips;  /.lingual  nerve,  to  the  mucous 
membraneof  the  anterior  two-thirds  of  the  tongue;  of,  auriculo-temporal  branch 
of  the  inferior  maxillary  division,  to  the  skin  of  the  anterior  part  of  the  exter- 
nal ear  and  adjacent  temporal  region;  x,  x,  x,  muscular  branches,  to  the  tcin 
poral,  masseter,  and  internal  and  external  ptervgoid  muscles:  //,  muscular 
branch,  to  the  mylo-hyoid  and  anterior  belly  of  the  diagastric ;  /,  sensitive 
branch  of  communication  to  the  facial  nerve. 

Destruction  of  the  sensory  root  results  in  complete  anaesthe- 
sia of  the  skin  of  the  face  and  mucous  membrane  of  the 
mouth. 


VI  NERVE,  211 

The  trophic  influence  of  the  sensory  root  is  of  very  great  value. 
If  it  be  divided,  the  complete  anaesthesia  of  the  conjunctiva, 
of  the  nostrils,  and  of  the  lips  prevents  the  reflex  self-protec- 
tion which  belongs  to  the  parts,  and  they  become  injured  very 
easily.  Aside  from  that,  the  direct  influence  upon  all  the 
parts  is  great,  so  that  when  it  is  cut  off  there  is  a  rapid  degen- 
eration resulting,  which  is  specially  apparent  in  the  mucous 
membrane  of  the  nose  and  in  the  cornea. 

Influence  of  the  sensory  branch  on  the  special  senses  :  (1)  Its 
division  causes  total  anesthesia  to  the  skin  and  mucous  mem- 
brane ;  the  loss  of  the  sense  of  touch  in  the  part  is  of  great 
importance,  for  the  tongue  and  lips  are  used  much  for  this 
purpose.  (2)  Upon  the  sense  of  sight  it  has  a  very  control- 
ling influence,  for,  as  we  have  seen,  the  trophic  influence  is 
essential  to  the  maintenance  of  the  integrity  of  the  eye.  (3) 
Upon  the  sense  of  smell.  Here  the  influence  is  the  same  as 
with  the  eyes,  trophic.  The  smell  is  soon  lost  on  account  of 
degeneration  of  the  mucous  membrane  after  division  of  the 
fifth  nerve.  (4)  Taste,  probably,  is  not  a  direct  function  of 
the  nerve ;  but  if  the  tactile  sensibility  is  gone  and  the  tro- 
phic changes  are  begun,  the  sense  of  taste  soon  disappears  in 
the  anterior  portion  of  the  tongue.  (5)  Upon  the  hearing 
the  effect  is  more  gradual  and  less  distinct.  The  secretions 
of  the  cavity  of  the  tympanum  and  of  the  external  auditory 
canal  are  of  great  importance  in  maintaining  normal  condi- 
tions. They  are  under  the  trophic  influence  of  the  fifth  nerve, 
both  through  its  auriculo-temporal  branch  and  through  its 
communication  with  the  otic  ganglion.  The  tensor  tympani 
muscle  is  also  supplied  by  the  motor  root.  Thus,  the  auditory 
apparatus  is  considerably  under  the  control  of  the  nerve. 

Symptoms  due  to  pathological  changes  in  the  sensory  root : 
Headaches  of  the  scalp  and  deeper  tissues,  and  more  especially 
the  frontal  sinuses,  are  common.  Toothache  and  facial  neu- 
ilgia  are  due  to  irritation  or  disease  of  parts  of  the  nerves. 
douloureux  is  a  persistent  neuralgia  of  some  or  all  of  the 

inches  of  the  nerve. 

VI  nerve  :  It  arises  from  a  nucleus  of  gray  matter  in  the 
floor  of  the  fourth  ventricle,  and  its  nucleus  is  more  or  less 
directly  connected  with  those  of  the  third,  fourth,  and  seventh 


212 


NERVOUS  SYSTEM. 


nerves.  It  emerges  without  decussation  at  the  posterior  border 
of  the  pons  Varolii,  and  passes  forward  to  the  orbit  with  the 
third  and  fourth  nerves.  In  its  course  it  has  many  commu- 
nications with  the  sympathetic  nerves,  but  their  significance 
is  unknown.  It  is  supplied  to  the  external  rectus  muscle  of 
the  eye,  and  its  stimulation  causes  external  squint,  and  paraly- 
sis causes  internal. 

VII  nerve :  It  arises  in  the  floor  of  the  fourth  ventricle, 
and  its  fibres  emerge  from  the  upper  part  of  the  groove  be- 

Fio.  103. 


Diagram  of  the  facial  nerve  and  its  distribution.  1,  facial  nerve  at  its  entrance  into 
the  internal  auditory  meatus :  2,  its  exit  at  the  stylo-mastoid  foramen;  3,4, 
temporal  and  posterior  auricular  branches,  distributed  to  the  muscles  of  the 
external  ear  and  to  the  occipilalis;  5,  branches  to  the  frontalis  muscle;  r>, 
branches  to  thestylo-hyoid  and  digastric  muscles  ;  7,  branches  to  the  upper  part 
of  the  platysma  myoides:  8,  branch  of  communication  with  the  superficial  cer- 
vical nerve  of  the  cervical  plexus. 

tween  the  olivary  and  restiform  bodies  in  company  with  the 
(eighth)  auditory  nerve  (sometimes  known  as  the  portin  mol- 
lis ;  the  facial  being  then  called  the  portio  dura  of  the  "sev- 
enth" pair,  when  the  classification  of  the  cranial  nerves  is 
made  into  nine  pairs).  It  passes  into  the  internal  auditory 


CHORDA    TYMPANI  BRANCH.  213 

canal,  and  escapes  from  the  skull  by  way  of  the  aqueduct  of 
Fallopius  and  the  stylo-mastoid  foramen. 

It  is  almost  wholly  a  motor  nerve,  and  is  distributed  to  all 
of  the  muscles  of  the  face  (Fig.  103)  except  those  mentioned 
as  controlled  by  the  motor  branch  of  the  trigeminus  nerve. 
The  muscles  of  the  eyelids  and  some  of  the  muscles  of  the 
palate  in  part  are  innervated  by  it,  as  well  as  the  parotid  and 
submaxillary  glands  through  the  chorda  tympani.  In  the  neck 
it  supplies  the  posterior  belly  of  the  digastric  and  the  platysma 
myoides  muscles.  It  also  sends  branches  to  the  stapedius 
muscle  of  the  internal  ear  and  to  all  of  the  muscles  of  the 
external  ear.  The  branches  passing  to  the  salivary  glands 
are  secretory  in  their  function ;  and  this  is  the  only  exception 
to  the  motor  influence  of  the  nerve. 

Function  of  the  VII  nerve :  It  is  the  motor  nerve  which 
parallels  in  its  distribution  the  sensory  root  of  the  fifth ;  it 
supplies  the  superficial  muscles,  as  the  latter  does  the  skin. 
It  is  the  nerve  of  "expression,"  by  which  the  features  are 
made  to  reflect  the  emotions. 

Paralysis  of  the  VII  nerve :  If  the  nerve  be  divided  or  dis- 
eased, the  face  of  that  side  is  devoid  of  motion  (Fig.  104), 
and  becomes  smooth  and  expressionless,  while  the  sound  side 
is  held  in  its  customary  pose.  The  eyelids  cannot  close  them- 
selves, and  the  lips  do  not  oppose  properly,  on  account  of  the 
defective  action  of  the  orbicular  muscle.  There  is  difficulty 
in  drinking  and  in  articulation  for  the  same  reason. 

The  eyelids  remain  open  in  facial  paralysis,  and  the  con- 
junctiva is  subject  to  injury  by  drying  and  by  foreign  bodies  ; 
but  the  injury  is  not  so  great  as  in  paralysis  of  the  fifth 
nerve,  because  the  seventh  has  no  trophic  influence. 

Chorda  tympani  branch :  The  chorda  tympani  is  a  small 
filament  given  off  from  the  facial  in  the  aqueduct  of  Fallo- 
pius, some  of  whose  fibres  are  distributed  to  the  submaxillary 
gland.  If  this  nerve  be  divided,  the  secretion  of  saliva  from 
the  gland  is  greatly  diminished,  while  stimulation  of  the 
nerve  will  excite  a  copious  flow.  This  is  an  active  secretion, 
and  is  not  a  simple  filtration  due  to  vaso-motor  changes.  A 
similar  influence  is  noted  in  the  corresponding  half  of  the 
tongue. 


214 


NERVOUS  SYSTEM. 


There  is  a  similar  distribution  of  fibres  from  the  facial  to 
the  parotid  gland,  which  also  receives  secretory  fibres  from 
the  glosso-pharyngeal  through  the  lesser  superficial  petrosal 


Fio  104. 


Facial  paralysis  of  the  right  side. 


nerve,  but  their  action  has  not  been  so  thoroughly  analyzed 
as  in  the  case  of  the  submaxillary  and  chorda  tympani. 

The  chorda  tympani  has  still  further  an  effect  upon  the 
sense  of  taste  in  the  anterior  portion  of  the  tongue.  If  it  be 
divided,  the  taste  is  much  blunted  on  the  affected  side.  It  is 


FUNCTION  OF  THE  IX  NERVE.  215 

now  known  that  this  is  due  to  the  communication  with  the 
glosso-pharyngeal  nerve,  thus  :  the  chorda  tympani  has  fibres 
from  the  otic  ganglion,  which,  in  its  turn,  receives  the  lesser 
superficial  petrosal  nerve  from  the  glosso-pharyngeal. 

IX  nerve :  It  arises  in  the  medulla  from  centres  near  those 
for  the  vagus  and  spinal  accessory  nerves.  Its  fibres  pass 
through  the  substance  of  the  medulla  and  emerge  in  com- 
pany with  those  of  the  vagus  and  spinal  accessory,  to  pass 
with  them  from  the  skull  through  the  jugular  foramen.  It 
gives  off  a  small  branch,  which  passes  to  the  tympanum  and 
Eustachian  tube  (Jacobson's  nerve)  while  in  the  jugular  fora- 
men, and  presents  a  small  ganglion,  the  petrosal ;  and  it  has 
communicating  branches  to  the  seventh  and  tenth  nerves  and 
to  the  otic  ganglion. 

The  nerve  divides  as  it  passes  down,  one  branch  passing 
forward  to  the  tongue,  and  one  going  to  the  pharynx  (whence 
its  name). 

The  portion  which  passes  to  the  tongue  is  distributed  to  the 
posterior  portion  of  the  organ,  to  the  circumvallate  papillae, 
and  the  mucous  membrane  behind  them,  some  fibres  going  to 
the  lining  of  the  soft  palate,  pillars  of  the  fauces,  and  tonsils. 
The  other  branch  is  distributed  to  the  mucous  membrane  of 
the  pharynx,  and  by  direct  branches  and  communication  with 
other  nerves  to  all  the  muscles  involved  in  swallowing. 

Function  of  the  IX  nerve :  (1)  It  is  the  nerve  of  taste;  and 
(2)  it  is  essentially  a  nerve  of  deglutition. 

(1)  It  is  only  in  the  latter  part  of  the  stay  of  food  in  the 
mouth  that  it  reaches  the  region  directly  supplied  by  this 
nerve.     When  the  food  is  to  be   swallowed,  it   is   pressed 
by  the  base  of  the  tongue  against  the  palate  arch  and  pushed 
into  the  pharnyx.     It  is  then  that  the  sense  of  taste  is  here 
exercised.      The    reflex    stimuli    then    excited  start  up    the 
motor  chain,  which  pushes  the  bolus  on  to  the  stomach.     At 
one  time  there  was  considerable  question  as  to  whether  the 
trigeminal  or  glosso-pharyngeal  was  really  the  conductor  of 
this  sense,  but  it  is  quite  likely  that  both  are  essential  to 
its  proper  appreciation. 

(2)  Whether  by  reason  of  its  communications  with  other 
nerves  or  not,  in  its  distribution  the  nerve  is  a  motor  nerve  as 


NERVOUS  SYSTEM. 

well  as  sensory.  Its  distribution  is  to  all  the  muscles  of 
deglutition,  and  stimulation  causes  contraction  of  the  muscles, 
while  division  paralyzes  them.  The  very  numerous  connec- 
tions of  the  nerve  complicate  its  anatomical  origin  very 
greatly,  and  interfere  with  a  clear  comprehension  of  the  un- 
aided function  of*  the  nerve. 

The  reflex  for  swallowing  originates  in  the  medulla  ob- 
longata,  where  the  origin  of  the  nerve  is  situated. 

X  nerve :  The  Xth  nerve  is  also  known  by  two  other 
names  :  "  pneumogastric,"  from  its  distribution  and  function  ; 
"  vagus "  or  "  par  vagum,"  from  its  scattered  distribution 
(vagus,  Latin,  wanderer). 

It  arises  from  the  gray  matter  in  the  floor  of  the  fourth 
ventricle,  its  nucleus  being  very  close  to  those  of  the  glnsso- 
pharyngeal  and  spinal  accessory.  Its  fibres  pass  through  the 
substance  of  the  medulla  oblongata,  and  emerge  from  its  lat- 
eral surface  with  the  roots  of  its  associate  nerves,  the  glosso- 
pharyngeal,  and  spinal  accessory.  It  passes  from  the  skull 
with  them  by  the  jugular  foramen.  It  has  at  this  point  a 
ganglionic  enlargement.  From  here  it  passes  down  the 
neck,  and  is  distributed  more  diffusely  than  any  other  cranial 
nerve. 

It  is  supplied  to  the  organs  by  which  air  and  food  enter 
the  body,  and  besides  this  has  several  important  connections 
with  the  sympathetic  system.  (1)  To  the  larnyx  it  supplies 
sensation  and  motion  through  the  superior  and  inferior  lari/n- 
geal  branches.  (2)  In  the  chest  it  forms  the  pulmonary 
plexuses,  which  innervate  the  bronchi  and  lungs.  (3)  Branches 
to  the  cardiac  plexus  supply  important  stimuli  to  the  heart 
and  great  vessels.  (4)  There  are  branches  to  the  pharyngeal 
and  cesophageal  plexuses  which  are  both  sensory  and  motor, 
supplying  both  the  mucous  membrane  and  the  muscular 
structures  of  the  parts.  (5)  Its  terminal  branches  supply 
the  sensory  and  motor  nerves  to  the  stomach,  the  left  nerve 
being  distributed  on  its  anterior  wall,  and  the  right  poste- 
riorly. (6)  Branches  also  pass  to  the  liver  and  spleen  and 
communicate  with  the  solar  plexus. 

Communication  between  X  nerve  and  other  nerves :  Soon 
after  leaving  its  origin  in  the  medulla  the  vagus  enters  into 


EFFECT  OF  SECTION  OF  X  NERVE  ON  RESPIRATION.    217 

so  many  communications  with  other  nerves,  both  sensory  and 
motor,  that  it  is  difficult  to  know  the  real  fibres  of  the  original 
root  and  to  determine  what  are  original  and  what  derived 
functions.  The  sympathetic  system  sends  fibres  in  all  the 
branches  of  the  pneumogastric,  and  the  pneumogastric  sends 
branches  to  many  of  the  important  sympathetic  plexuses  and 
ganglia ;  the  pharyngeal,  laryngeal,  resophageal,  pulmonary, 
cardiac,  and  solar  plexuses  are  so  made  up  by  branches  from 
both.  The  spinal  accessory  nerve  is  an  important  contributor, 
in  that  it  sends  a  large  branch  which  is  incorporated  in  the 
vagus.  The  fibres  from  the  spinal  accessory  nerve  are  motor, 
and  are,  most  of  them,  carried  in  the  recurrent  laryngeal 
nerve.  There  are  also  communications  to  the  glosso-pharyn- 
geal  and  hypoglossal  nerves,  and  it  also  receives  motor  fibres 
from  the  facial  and  upper  two  cervical  nerves. 

The  original  nerve  is  probably  entirely  sensory,  and  its 
motor  function  is  derived  from  these  connections  with  motor 
nerves. 

Function  of  X  nerve  in  respiration :  The  nerve  supplies,  as 
has  been  said,  the  motor  and  sensory  functions  of  the  larynx, 
and  in  this  is  of  value  to  the  respiratory  function  both  in  the 
prevention  of  foreign  substances  entering  the  rima  glottidis, 
and  in  the  opening  of  that  orifice  for  the  entrance  of  air. 
Besides  this,  it  supplies  sensory  fibres  to  the  pulmonary 
plexus  which  transmit  the  reflex  stimulus  to  the  medulla,  by 
which  the  motor  apparatuses  excited  to  action. 

The  muscles  of  the  larynx  involved  in  the  production 
of  sound  are  supplied  by  this  nerve,  and,  as  the  approxi- 
mation of  the  chordae  vocales  is  necessary  for  this,  it  fol- 
lows that  the  voice  is  dependent  upon  the  fibres  of  the 
pneumogastric  supplied  by  the  inferior  or  recurrent  laryn- 
geal nerve. 

Effect  of  section  of  X  nerve  on  respiration :  Respiration  is 
slowed  immediately  to  about  half  its  usual  rate,  and  soon 
drops  to  five  or  six  to  the  minute,  and  even  slower.  The 
respiration  is  easy — inspiration  slow  and  full,  expiration 
harsh  and  sudden.  Death  follows  this  operation  in  a  short 
time  (one  to  six  days),  and  the  animal  during  the  time  is 
sluggish  and  apparently  suffers  from  slow  carbonic-oxide 


218  NERVOUS  SYSTEM. 

narcosis.  It  is  inferred  from  this  that  the  vagus  is  the  nerve 
which  carries  to  the  automatic  centre  the  stimuli  which  are 
needed  to  keep  up  the  automatism,  and  that  the  medulla  is 
incapable  of  originating  the  motor  impulses  unless  controlled 
by  afferent  stimuli. 

Function  of  X  nerve  in  deglutition:  Deglutition  both  in  the 
pharynx  and  the  oesophagus  is  under  the  influence  of  the 
vagus,  which  gives  innervation  directly  to  the  thoracic  part 
of  the  latter  and  through  the  inferior  laryngeal  branch  to  the 
cervical  part.  The  sensory  fibres  act  as  conductors  of  the 
stimulus  which  results  in  the  reflex  peristalsis  by  which  the 
food  is  carried  on  through  the  oesophagus.  The  sensory  dis- 
tribution to  the  larynx  must  not  be  forgotten  in  this  connec- 
tion, for  by  it  food  is  kept  from  the  respiratory  organs.  Sec- 
tion of  the  vagi  causes  paralysis  of  swallowing,  and  food  is 
apt  to  pass  the  glottis  on  an  attempt  to  swallow,  not  even  a 
cough  being  excited  by  such  an  accident.  The  closure  of  the 
glottis  in  swallowing  is  caused  by  a  reflex  action  known  as 
the  "action  of  arrest,"  and  is  derived  from  the  sensory  fibres 
of  the  vagus. 

Relation  of  X  nerve  to  stomach :  The  stomach  receives  both 
motor  and  sensory  function  through  the  vagus.  The  stomach 
receives  its  warning  of  the  presence  of  food  through  the  sen- 
sory fibres,  and  the  muscular  fibres  excite  the  organ  to  con- 
tract upon  it  and  "  churn  "  it  about  during  digestion.  There 
is  also  a  vaso-motor  influence  derived  from  the  vagus.  AVhen 
the  nerve  is  cut  but  little  food  can  reach  the  stomach,  because 
of  the  paralysis  of  the  oesophagus,  and  what  food  does  enter 
is  digested  very  slowly,  so  that  the  function  of  the  pncu mo- 
gastric  may  be  considered  essential  to  stomach  digestion. 
The  connection  with  the  solar  plexus  also  involves  the  intes- 
tines in  the  action  of  the  vagus. 

Influence  of  X  nerve  on  the  heart:  There  are  numerous 
branches  to  the  cardiac  plexus  from  the  trunk  of  the  vagus 
and  from  its  inferior  laryngenl  branch.  Stimulation  of  the 
pheumogastric  nerve  diminishes  the  frequency,  or,  if  strong, 
entirclv  stops  the  heart  in  diastole.  The  nerve  is  therefore 
regarded  as  having  an  inhibitory  (trfion.  'Phis  is  an  nnnsual 
effect,  for  in  other  cases  the  stimulation  of  nerves  going  to 


FUNCTION  OF  XI  NERVE.  219 

muscles  causes  contraction :  the  heart,  however,  becomes 
flaccid  under  the  influence  of  the  stimulated  vagus. 

Other  functions  of  X  nerve  :  The  vagus  nerve  is  the  channel 
for  excito-motor  reflexes  in  coughing  and  vomiting,  as  well 
as  for  many  other  less  essential  reflexes,  such  as  sighing, 
hiccoughing,  and  the  like. 

XI  nerve  :  The  origin  of  the  Xlth  nerve  is  twofold.  One 
root  arises  in  the  gray  matter  of  the  medulla  near  the  nucleus 
for  the  vagus,  while  the  other  arises  from  the  lateral  tract  of 
the  cord  as  low  as  the  fifth  or  sixth  cervical  vertebra,  and 
passes  up  between  the  anterior  and  posterior  spinal  nerve-roots 
to  join  the  medullary  (or  accessory)  portion  at  its  emergence 
from  the  medulla.  The  united  nerve  soon  divides  and  passes 
out  through  the  jugular  foramen  with  the  glosso-pharyngeal 
and  pneumogastric  nerves,  the  medullary  portion  joining  the 
trunk  of  the  pneumogastric,  wrhile  the  spinal  root  supplies  the 
sterno-mastoid  and  trapezius  muscles. 

Function  of  XI  nerve :  The  nerve  is  a  motor  to  all  intents, 
though  it  has  some  sensory  fibres,  as  is  shown  by  the  pain 
caused  by  pinching  it. 

(1)  The  anastomatic  branch,  which  joins  the  pneumogastric, 
is  apparently  largely   given  off  in  the    recurrent  laryngeal 
nerve ;  but  its  section  does  not  produce  the  same  effect  upon 
the  larynx  as  section  of  the  trunk  of  the  vagus  or  of  its  in- 
ferior laryngeal  branch.     There  is  paralysis  of  the  voice,  but 
not  of  the  movements  of  the  glottis  for  respiration.     There 
are  probably  some  fibres  of  this  nerve  also  given  off  to  the 
cardiac  plexus. 

(2)  The  muscular  branch  supplies  the  sterno-mastoid  and 
trapezius  muscles;  but  these  muscles  are  also  supplied  by  the 
cervical  spinal  nerves,  and  their  action  is  not  paralyzed  by 
the   section   of  this  branch  of  the  spinal  accessory.     It   is 
found,  however,  that  the  relation  of  these  muscles  to  respira- 
tion is  impaired  by  isolation  from  this  nerve — that  is,  when 
the  breath  is  held  in  any  violent  exertion,  as  straining  or 
pushing,  or  when  a  loud  cry  is  uttered,  the  sterno-mastoid 
and  trapezius  muscles  contract  to  fix  the  head  and  hold  the 
spine   steady.     This  action   seems  to  be  prevented    by  the 
section  of  this  muscular  branch  of  the  spinal  accessory. 


220  THE  SENSES. 

XII  nerve :  It  arises  in  the  gray  matter  at  the  inferior 
extremity  of  the  floor  of  the  fourth  ventricle,  mesial  to  the 
origin  of  the  spinal  accessory  and  pneumogastric  nerves. 
The  fibres  pass  through  the  substance  of  the  medulla  ob- 
longata,  between  the  pyramid  and  the  olivary  body,  and, 
emerging  in  a  number  of  small  bundles,  connect  into  a  nerve- 
trunk  which  emerges  from  the  skull  by  the  anterior  condyloid 
foramen.  It  passes  down  the  neck  to  about  the  level  of  the 
hyoid  bone,  where  it  curves  forward  and  into  the  tongue, 
giving  off  branches  to  the  muscles  which  move  that  organ. 

Function  of  XII  nerve :  It  is  a  motor  nerve,  but  po>- 
some  sensory  fibres  derived  from  the  cervical  spinal  nerves 
and  from  the  trigeminus,  with  whose  lingual  branch  it  inos- 
culates on  the  side  of  the  tongue.  Filaments  from  it  arc 
distributed  to  all  the  muscles  which  move  the  tongue,  and  to 
the  depressors  of  the  hyoid  bone  through  its  descendiixj 
branch. 

The  latter  branch,  although  in  the  anatomical  sheath  with 
the  hypoglossal  nerve,  is  not  an  integral  part  of  the  nerve, 
but  is  derived  from  the  upper  cervical  nerves. 

Influence  of  XII  nerve  on  digestion  :  It  is  important  in  mas- 
tication, for  its  muscles  move  the  food  about  for  the  better 
action  of  the  teeth.  In  animals,  after  division,  drinking  is 
impossible,  because  they  are  unable  to  lap  up  fluids,  and  the 
food  is  swallowed  with  difficulty  because  it  is  not  carried  back 
into  the  pharynx  by  the  tongue  after  mastication. 

Connection  of  XII  nerve  with  speech :  Articulation  of  most 
sounds  involves  movements  of  the  tongue.  Impaired  articu- 
lation is  an  early  symptom  in  bulbar  or  glosso-labio-laryn- 
geal  paralysis. 

THE  SENSES. 

A  peripheral  organ  for  the  reception  of  an  impression,  a 
nerve  for  its  conduction,  and  a  centre  in  the  brain  for  the 
perception,  are  the  organs  necessary  for  sensation.  It  i>  by 
means  of  impressions  so  received  and  conducted  to  it  that  the 
mind  is  able  to  control  the  body  and  to  take  cognizance  of  the 
external  world. 


COMMON  AND  SPECIAL  SENSATIONS.  221 

Classification  of  sensations  :  Common  sensations  and  special 
sensations.  These  last  are  commonly  called  "  the  senses." 

Common  sensations :  Such  perceptions  as  cannot  be  dis- 
tinctly located  in  any  organ  or  set  of  organs,  such  as  fatigue, 
hunger,  thirst,  satiety.  Besides  these,  there  are  some  sensa- 
tions which  involve  certain  organs  which  must  be  classed 
under  this  head ;  thus  inclinations  to  cough  or  to  sneeze  or 
to  vomit  are  common  sensations,  and,  similarly,  to  urinate  or 
defecate.  Many  of  these  sensations  occupy  a  border-line  be- 
tween common  sensibility  and  the  special  sense  of  touch,  such 
as  itching  and  tickling. 

Pain  is  a  common  sensation,  but  is  very  closely  allied  to 
the  sense  of  touch.  The  two  may  be  differentiated,  however. 
If  one  touch  a  sharp  instrument,  he  may  perceive  its  shape 
and  condition ;  but  if  the  pressure  be  increased,  the  ability 
to  perceive  its  form  is  lost,  and  instead  the  sensation  of  pain 
is  established.  The  relation  of  the  two  is  curiously  shown 
in  partial  anaesthesia  by  drugs,  as  when  one  takes  nitrous- 
oxide  gas  for  the  extraction  of  a  tooth,  and  is  able  to  feel  the 
operation  and  to  know  what  has  been  done,  without  in  the 
least  feeling  pain. 

The  seat  of  the  senses  is  the  brain,  or  sensorium.  The  organ 
of  the  mind,  which  perceives  the  thing  which  the  organ  of 
sense  has  taken  an  impression  from,  is  the  fundamental  struct- 
ure in  the  necessary  chain. 

Hallucination  is  the  perception  of  an  object  as  a  real  presence 
without  the  presence  of  the  object  to  justify  the  perception  ; 
that  is,  it  is  an  act  of  the  brain  which  refers  its  action  to  an 
organ  of  the  senses.  Thus,  in  delirium  tremens  a  person  may 
perceive  many  curious  and  uncanny  things,  which  his  mind 
hears  and  sees  and  feels,  but  which  his  senses  could  not 
take  cognizance  of,  because  they  are  only  "  creatures  of  the 
mind." 

Difference  between  common  and  special  sensations :  The 
most  important  distinction  between  common  and  special  sen- 
sations, is  that  the  former  are  strictly  limited  to  the  condition 
of  our  bodies,  while  by  the  latter  we  gain,  in  addition,  infor- 
mation respecting  affairs  outside  of  our  bodies.  This  differ- 
ence may  be  explained  if  we  compare  the  sensations  of  pain 


222  THE  SENSES. 

and  touch,  the  one  a  common,  the  other  a  special  sensation. 
For  example,  if  the  point  of  a  needle  be  gently  pi 
against  the  tip  of  the  finger,  we  only  feel  this  point  by  our 
sense  of  touch  and  refer  the  sensation  to  the  object  causing 
it.  But  if  the  needle  be  pressed  harder,  so  as  to  enter  the 
skin,  we  feel  at  once  a  sensation  of  pain,  which  is  no  longer 
referred  to  the  needle,  but  to  the  finger  itself.  The  sensation 
of  pain  is  not  able  to  cause  us  to  recognize  the  object  which 
caused  it,  nor  its  nature. 

Sensations  and  perceptions :  Our  habit  of  referring  sensa- 
tions to  outside  causes  leads  us  to  consider  as  properties  of 
external  bodies  the  sensations  which  they  excite  in  us.  "When 
we  speak  of  anything  as  having  a  bad  taste,  we  forget  that 
it  only  tastes  bad  to  us.  This  habit  pertains  especially  to 
sensations  of  touch  and  sight.  From  constant  exercise  of  it 
we  finally  come  to  believe  implicitly  in  the  "  evidence  of  our 
senses." 

Judgments  :  There  is  a  distinction  between  a  sensation  and 
a  judgment  (which  is  often  unconsciously  based  on  sensations). 
When  we  estimate  the  distance  of  an  object  from  ourselves 
we  form  a  judgment  based  on  past  experience  of  many  sensa- 
tions, such  as  the  number  of  steps  we  must  take  before  we 
touch  it,  etc. 

Nerves  of  special  sense:  The  special  nerves  have  no  other 
function  than  the  special  one  for  which  they  are  set  apart  ; 
and  when  they  are  separated  from  their  special  orpins  for 
receiving  impressions,  they  no  longer  respond  to  the  custom- 
ary stimuli.  The  special  senses  are  touch,  taste,  smell,  hearin</, 
and  sight 

Touch. 

The  organ  of  touch  consists  of  the  skin  and  mucous  mem- 
branes adjoining  it.  The  nails  and  teeth  too  exercise  a  peculiar 
function  in  this  regard,  and  the  hair  in  some  regions — c.  //., 
eyelashes.  Touch  is  really  only  a  specialized  development  of 
common  sensation  or  sensibility.  The  sensations  of  touch, 
therefore,  are  conveyed  to  the  central  nervous  system  by 
those  nerves  which  confer  ordinary  sensation  on  the  differ- 


MEASURE  OF  ACUTENESS  OF  TOUCH.  223 

ent  parts  of  the  body — that  is,  the  sensory  cerebral  nerves 
and  those  arising  from  the  posterior  roots  of  the  spinal 
nerves.  By  means  of  the  sense  of  touch  we  acquire  knowl- 
edge of  the  size,  shape,  and  other  external  peculiarities  of 
bodies. 

Varieties  of  touch  :  (1)  Tactile  sensibility,  or  touch  proper ; 
(2)  the  sense  of  pressure  or  weight ;  (3)  the  sense  of  temper- 
ature. All  of  these,  when  carried  beyond  moderate  limits, 
are  merged  into  the  sensation  of  pain. 

Acuteness  of  touch :  The  distribution  of  the  end-organs  of 
the  sensory  nerves  varies  in  different  parts  of  the  body,  and 
the  more  numerous  the  touch-corpuscles,  the  more  acute  the 
sensibility  of  the  part.  Again,  the  thickness  of  the  epidermis 
has  marked  influence  in  determining  the  tactile  ability,  por- 
tions of  the  hands  and  feet,  when  callous,  having  very  blunted 
sensibility.  The  hardness  and  elasticity  of  bodies,  the  quality 
of  the  surface  as  to  smoothness,  the  size  and  form  and  the 
temperature,  and  wet  or  dry  condition,  are  all  easily  deter- 
mined by  touch. 

The  hand  is  of  great  value  as  an  organ  of  touch  because 
of  the  acuteness  of  its  sensibility.  Further  than  this,  the 
hand  is  so  constructed  as  to  be  capable  of  forming  impres- 
sions of  bodies  by  reason  of  its  power  to  grasp  them  and  to 
test  them  as  to  weight. 

Measure  of  acuteness  of  touch  is  by  means  of  a  pair  of  com- 
passes whose  points  are  blunted.  The  legs  of  the  instrument 
are  separated,  and  the  distance  between  the  points  which  can 
just  be  distinguished  as  two  separate  contacts,  measures  the 
sensibility.  From  the  accompanying  table  it  will  be  seen 
that  the  touch  is  most  acute  in  the  tip  of  the  tongue  and  in 
the  fingers  and  tips,  while  in  other  portions  the  sense  of  touch 
is  so  vague  that  two  points  of  contact  are  not  distinguished 
until  they  are  two  and  a  half  inches  apart.  It  is  found  that 
the  points  of  the  compasses  must  be  more  widely  separated 

Iwhen  the  test  is  made  in  the  long  axis  of  a  limb  than  when 
across  it  (the  table  is  from  Kirke's  Handbook) : 


224  THE  SENSES. 

Table  of  Variations  in  the  Tactile  Sensibility  of  the  Different 
Partff. — (The  measurement  indicates  the  least  distance 
at  which  the  two  blunted  points  of  a  pair  of  compa— <  - 
could  be  separately  distinguished. — E.  H.  Weber.) 

Tip  of  tongue £(  inch. 

Palmar  surface  of  third  phalanx  of  forefinger  .    .    .  T^ 

Palmar  surface  of  second  phalanges  of  fingers    .    .    .  £ 

Red  surface  of  under  lip £ 

Tip  of  the  nose £ 

Middle  of  dorsum  of  tongue 

Palm  of  hand fy 

Centre  of  hard  palate £ 

Dorsal  surface  of  first  phalanges  of  fingers ^2 

Back  of  hand l| 

Dorsum  of  foot  near  toes 1£     " 

Gluteal  region l|     " 

Sacral  region l|     " 

Upper  and  lower  parts  of  forearm 1£     " 

Back  of  neck  near  occiput 2       " 

Upper  dorsal  and  mid-lumbar  regions 2       " 

Middle  part  of  forearm 2j     " 

Middle  of  thigh 2|     " 

Mid-cervical  region 2^     " 

Mid-dorsal  region 2J     " 


The  sense  of  touch  may  be  greatly  educated  and  special- 
ized. This  is  seen  in  many  of  the  arts  where  great  dex- 
terity obtains  by  reason  of  an  educated  touch.  The  read- 
ing raised  letters  by  the  blind  is  a  familiar  example  of  edu- 
cated touch. 

Pressure-sensation:  When  weight  is  added  to  an  ordinary 
touch  the  sensation  of  the  pressure  of  the  weight  is  felt,  and 
by  it  one  can  judge  with  considerable  accuracy  the  amount  of 
the  pressure,  and  determine  the  comparative  pressure  of  two 
weights  with  approximate  correctness  within  limits  of  press- 
ure. This  is  known  as  the  sense  of  pressure. 

Muscular  sense:  By  taking  a  body  in  the  hand  and  raising 
it  we  feel  a  sense  of  resistance  in  the  muscles,  by  whose  in- 
tensity we  can  much  more  accurately  determine  the  weight. 
This  is  the  muscular  sense.  It  is  developed  to  an  exceedingly 
fine  degree  in  some  occupations;  for  example,  postal  clerks 
detect  overweight  letters  with  wonderful  accuracy  and  quick- 
ness. 


TASTE.  225 

It  has  been  urged  that  the  muscular  sense  is  of  central 
origin,  and  depends  upon  the  strength  of  the  impetus  which 
must  be  sent  to  the  muscles  to  cause  them  to  do  certain  work. 
It  may,  however,  be  due  to  a  training  of  the  sensibility  of 
the  muscle,  whereby  the  relative  strength  of  a  contraction  is 
perceived  as  a  sensation.  The  centre  for  muscular  sense  is  in 
the  upper  part  of  the  quadrate  lobule  on  the  mesial  surface 
of  the  hemisphere.  Its  involvement  by  pressure  brings  about 
inability  to  locate  the  position,  say,  of  hand  or  foot  without 
the  aid  of  sight.  Thus,  the  individual  can  move  his  upper 
extremity ;  but  if  the  hand  is  placed  out  of  range  of  vision, 
he  does  not  know  where  it  is. 

Temperature-sense :  The  surface  of  the  body  is  very  sen- 
sible of  temperature-changes ;  and  that  this  is  distinct  from 
ordinary  tactile  sensation  has  been  inferred  from  the  fact  that 
when  the  ordinary  touch  is  blunted  the  temperature-sense 
may  remain  unimpaired.  Temperature-sensations  are  not 
accurate ;  they  are  only  relative — that  is,  we  infer  from  the 
temperature  of  the  skin  or  of  our  habitual  surroundings  the 
warmth  or  coldness  of  the  thing  tested.  It  is  related  that 
Arctic  explorers  have  found  the  water  feel  warm  when  swim- 
ming in  pools  on  icebergs,  and  a  drop  of  the  mercury  to  80° 
F.  is  said  to  feel  cold  in  torrid  climates.  A  more  simple 
illustration  is  that  of  immersing  one  hand  in  water  at  40°  F. 
and  the  other  in  water  at  120°  F.,  and  then  both  in  water  at 
80°  F.,  when  one  hand  will  feel  hot  and  the  other  cold, 
though  both  are  subjected  to  the  same  temperature.  Again, 
during  a  chill  the  temperature  of  the  body  is  often  very  con- 
siderably elevated,  and  yet  the  sensation  is  entirely  of  cold. 

Taste. 

Taste — necessary  conditions:  Aside  from  the  conditions 
which  are  always  necessary  for  sense-perception — viz.,  proper 
organs  for  receiving,  communicating,  and  perceiving  the  sen- 
sory impulse — there  must  be  present  a  sapid  substance  which 
must  be  in  solution.  The  solution  in  the  case  of  dry  sub- 
stances is  effected  by  the  saliva.  It  is  also  necessary  that  the 
surface  of  the  organs  of  taste  shall  be  moist.  The  substances 

15— Phys. 


226  THE  SENSES. 

which  excite  the  special  sensation  of  "taste"  act  by  produc- 
ing a  change  in  the  condition  of  the  terminal  filaments  of  the 
gustatory  nerve,  and  this  change  furnishes  to  it  the  required 
stimulus. 

Origin  of  taste :  Chiefly  from  the  tongue,  though  there  is 
some  power  to  taste  resident  in  the  soft  palate,  fauces,  tonsils, 
and  pharynx.  In  the  tongue  the  taste  is  more  acutely  devel- 
oped in  the  posterior  portion,  though  in  most  the  tip  and 
sides  are  sensitive  to  taste.  The  central  portion  of  the  dor- 
sum  is  not  an  actively  sensitive  taste-organ.  The  under  sur- 
face of  the  tongue  is  little  if  at  all  sensitive  to  taste. 

The  nerve-supply  for  sense  of  taste  is  probably  the  glosso- 
pharyngeal.  The  lingual  branch  of  the  fifth  (or  "  gustatory  ") 
is  also  a  conductor  of  taste-impressions  for  the  front  of  the 
tongue,  but  by  means  of  the  fibres  from  the  chorda  tympani 
and  otic  ganglion  (see  page  172). 

The  tongue  is  a  flattened  muscular  organ  covered  by  epithe- 
lium. It  is  controlled  by  intrinsic  and  extrinsic  muscles, 
which  give  it  a  remarkable  flexibility  of  movement ;  the 
latter  for  its  larger,  and  the  former  for  its  more  delicate 
actions. 

There  are  three  varieties  of  papilla  found,  which  are 
known  as  filiform,  fungiform,  and  circumvallate  papilla?. 
These  are  set  chiefly  upon  the  dorsum  of  the  tongue; 
and  over  its  whole  surface  are  numerous  mucous  follicles, 
whose  secretions  keep  the  tongue  moist  (Figs.  105,  106, 
and  107). 

The  filiform  papillce  are  set  upon  the  middle  of  the  dorsum, 
and  are  scattered  over  the  entire  surface,  and  are  far  more 
numerous  than  any  other  kind.  They  are  conical  in  shape, 
and  are  covered  with  epithelium,  which  projects  in  a  brush- 
like  tuft  from  the  apex.  Their  function  is  mostly  tactile, 
and  in  animals,  especially  of  the  cat  tribe,  are  very  promi- 
nent. 

The  fa/nffiform  papUlcc  are  chiefly  distributed  over  the  sides 
and  tip  of  the  organ,  and  sparsely  upon  the  dorsum.  They 
are  larger  at  tin- surface  than  at  the  base,  club-shaped,  and 
arc  supplied  with  bloodvessels  and  nerves.  Their  function  is 
probably  sciiH.ry  (Fig.  106). 


OTHER  SENSATIONS  IN   THE  TONGUE.  227 

The  circumvallate  papillae  are  somewhat  similar  in  shape  to 
the  fungi  form,  but  considerably  larger.  They  are  situated  at 
the  posterior  portion  of  the  dorsum  in  a  V-shaped  arrange- 
ment, and  number  only  eight  or  ten.  Around  the  circum- 

FIG.  105. 


Upper  surface  of  the  tongue. 


valla  te  papillse  are  the  taste-goblets,  or  gustatory  buds,  which 
are  the  form  of  nerve-ending  characterizing  the  parts  where 
this  sense  is  developed  (Fig.  107). 

Other  sensations  in  the  tongue :  The  sense  of  touch  is  very 
highly  developed  here,  and  with  it  the  sense  of  temperature, 
pressure,  pain,  etc.:  upon  these  tactile  and  muscular  senses  to 


228 


THE  SENSES. 


a  great  extent  depend  the  accuracy  of  the  tongue  in  many  of 
its  important  uses — speech,  mastication,  deglutition,  sucking. 


FIG.  106. 


B 


Surface  and  sectional  view  of  a  fungiform  papilla.  A,  the  surface  of  a  fungiform 
papilla  partiallv  denuded  of  the  epithelium  (3o  diameters) :  p,  secondary  papillae; 
a,  epithileum.  "B,  section  of  a  " 


a,  artery  ;  t>,  vein ;  c,  capillar 
ered  by  epithelium  (from  K6 


a  fungiform  papilla  with  the  bloodvessels  injected: 
•y  loops  of  simple  papillae  in  the  neighborhood,  cov- 
lliker,  after  Todd  and  Bowman). 


The  tactile  sense  is  very  important,  too,  in  the  sense  of  taste, 
for  with  many  substances  the  taste  is  largely  due  to  their  me- 


Vertical  section  of  a  circnmvallate  papilla,  from  the  calf  (35  diameters).  A,  the 
papilla;  B,  the  adjacent  surface.  The  figure  shows  the  nerves  of  the  papilla 
spreading  toward  the  surface  and  toward  the  taste-buds  which  are  imbedded 
in  the  epithelium  at  the  sides;  in  the  sulcus  on  the  left  the  duct  of  a  gland 
is  seen  to  open  (Engelmann). 

chanical  condition  :  this  is  the  case  with  mucilaginous,  oily, 
and  chalky  tastes. 

Association  of  smell  and  taste  :   It   is  important,  for  with 
many  substances — particularly  aromatic  substances — of  food 


SMELL.  229 

and  drink  the  association  of  smell  and  taste  is  very  essential 
to  a  thorough  appreciation  of  a  flavor.  Most  cooked  foods 
lose  their  savor  if  the  nose  is  obstructed  ;  thus  with  a  "  cold  " 
in  the  nose  "  everything  tastes  alike." 

The  principal  tastes  are  sweet,  bitter,  acid,  alkaline,  and 
saline.  Besides  these,  the  general  sensibility  of  the  tongue 
detects  pungent  or  caustic  and  styptic  tastes,  as  well  as  the 
oily  and  mucilaginous  tastes. 

Sensibility  of  tongue  :  It  is  quite  acute.  A  solution  of  acid 
or  bitter  substances  is  tasted  when  very  dilute  :  strychnine  is 
said  to  be  tasted  in  a  1  :  600,000  solution ;  sulphuric  acid, 
1  : 1000. 

After-taste :  After  an  aromatic  substance  has  been  tasted 
there  remains  in  the  mouth  an  impression  of  that  flavor ;  and 
if  such  substances  be  taken  in  rapid  succession,  the  apprecia- 
tion of  their  flavor  is  lost.  This  impression,  which  is  left  by 
a  strong  flavor,  is  called  the  after-taste,  and  is  utilized  some- 
times to  cover  the  taste  of  a  disagreeable  medicine,  a  strongly 
flavored  aromatic  preceding  it. 

Smell. 

Smell — conditions  :  The  first  essentials  are  a  special  nerve 
and  nerve-centre,  the  changes  in  whose  condition  are  per- 
ceived as  sensations  of  odor.  No  other  nerve-structure  is 
capable  of  such  sensations,  even  when  acted  on  by  the  same 
cause.  The  special  organs  for  this  sense  for  the  reception, 
conduction,  and  perception  of  the  stimulus,  as  in  the  case  of 
any  of  the  senses,  must  be  in  their  normal  condition,  and  a 
stimulus  (an  odor)  must  be  present  to  excite  them. 

Odors  are  caused  either  by  minute  particles  of  solid  matter 
or  by  gases  which  are  in  the  atmosphere,  and  they  must  be 
capable  of  solution  in  the  mucus  of  the  Schneiderian  mem- 
brane. The  substance  must  pass  in  a  current  of  air  through 
the  nostrils  or  it  is  not  perceived  as  an  odor.  This  is  accom- 
plished by  "  sniffing"  the  air,  and  thus  creating  an  intermit- 
ting current  which  is  tested  by  the  olfactory  sense.  In  this 
way  a  trace  of  a  gas  or  impalpable  powder  may  be  de- 
tected which  cannot  be  traced  by  chemical  or  other  means. 


230 


THE  SENSES. 


If  the  substance  be  applied  as  a  solution,  it  is  not  detected  ; 
thus,  rose-water  in  a  nasal  douche  is  not  noticed  while  the 
nostrils  are  full  of  fluid,  and  yet  as  soon  as  the  nostrils  are 
free  the  odor  appears. 

The  olfactory  nerves  are  the  functional  nerves  of  the  sense, 
and  are  spread  out  in  a  fine  network  (Fig.  109)  over  the  sur- 

FIG.  108. 


Cells  and  terminal  nerve-fibres  of  the  olfactory  region,  highly  magnified.     1,  from 
the  frog;  2,  from  man:  a,  epithelial  cell,' extending  deeply  into  a  ramified 

peripheral  rods  ;  e,  their  extremities,  seen 
their  central  filaments  ;  3,  olfactory  ni-rvr- 
fibrilUe  (Frey,  after  Schultze). 


tne  irog;  z,  irom  man:  a,  epitneiiai  ceil,' exi 
process  ;  b,  olfactory  cells  :  c,  their  peripheral 
in  1  to  be  prolonged  into  fine  hairs ;  d,  their  cent 
fibres  from  the  do}  ;  n,  the  division  into  fine  fi 


face  of  the  superior  turbinated  bone  and  on  the  upper  third 
of  the  septum.  The  nerves  end  in  special  end-organs,  known 
as  olfactory  celts  (Fig.  108),  which  lie  under  the  ciliated  epithe- 
lium of  the  part. 

Origin  of  olfactory  nerves:  The  nerves  arise  from  a  mass  «>!' 
gray  matter  lying  beneath  the  anterior  lobe  of  the  brain  upon 


ORIGIN  OF  OLFACTORY  NERVES. 


231 


the  cribriform  plate  of  the  ethmoid  bone.  This  is  the  olfac- 
tory bulb,  and  it  is  connected  by  the  olfactory  tract  with  the 
cerebrum.  Each  olfactory  tract  arises  from  the  cerebrum  by 
three  roots,  two  of  which  are  composed  of  white  matter,  the 
other  largely  of  gray  matter.  By  these  it  is  connected  with 
the  olfactory  centres. 

The  lining  membrane  of  the  nasal  cavity  is  very  sensitive 
to  irritation,  the  nasal  branch  of  the  fifth  nerve  and  branches 
from  the  spheno-palatine  ganglion  furnishing  the  ordinary 

FIG.  109. 


Distribution  of  nerves  in  the  nasal  passages;  1,  olfactory  bulb,  with  its  nerves; 
2.  nasal  branch  of  the  fifth  pair  ;  3,  spheno-palatine  ganglion. 

and  tactile  sense.  Therefore  we  can  perceive,  by  the  nose, 
the  sensations  of  cold,  heat,  itching,  tickling,  pain,  and  ten- 
sion or  pressure. 

The  perceptions  of  the  olfactory  and  of  the  nerves  of  touch 
often  resemble  each  other,  and  some  stimuli  affect  both  nerves. 
The  common  sensibility  is  evoked  by  such  substances  as  are 
irritating  and  acrid  :  ammonia  gas  has  no  odor,  but  it  stimu- 
lates the  mucous  membrane  by  its  irritating  properties.  The 
tactile  or  common  sensibilities  remain  when  the  olfactory  are 
gone.  The  relation  between  the  two  kinds  of  perception  is 


232  THE  SENSES. 

lost  to  us,  and  we  speak  of  the  smell  of  ammonia  or  of  alco- 
hol when  it  is  probably  not  an  olfactory,  but  a  sensory,  per- 
ception. 

Acuteness  of  smell :  The  sense  of  smell  is  very  acute,  but 
not  so  sharp  in  man  as  in  many  of  the  lower  animals.  The 
distribution  of  the  olfactory  nerves  is  much  wider  in  some  of 
the  animals,  and  the  cerebral  development  is  correspondingly 
increased.  In  man  the  range  of  susceptibility  is,  however, 
probably  greater.  The  variety  of  odors  and  the  very  minute 
quantity  of  stimulant  substance  required  to  produce  a  sensa- 
tion of  smell  are  quite  wonderful.  The  most  delicate  analy- 
sis may  fail  to  show  traces  of  the  substances  which  can  be 
appreciated  by  the  sense  of  smell.  For  instance  0.000000005 
gramme  of  oil  of  peppermint  in  1  litre  of  air  can  be  appreci- 
ated. 

There  are  some  odors  pleasant  to  some  which  others  find 
almost  intolerable.  Musk,  for  example,  is  a  pleasant  per- 
fume to  some,  while  to  others  it  is  quite  unendurable.  In 
the  same  way,  the  acuteness  of  this  sense  in  some  is  more 
marked  than  in  others,  and  yet  this  may  apply  only  to  certain 
kinds  of  odors.  Like  the  sense  of  touch  and  the  other  special 
senses,  that  of  smell  can  be  very  much  developed  by  practice. 
Large  salaries  are  paid  to  experts  in  discrimination  of  the 
quality  of  wines,  etc.  Often  in  cases  of  mental  disease  there 
are  hallucinations  of  smell,  which  also  may  occur  in  cases  of 
disease  of  the  olfactory  centres,  when  there  may  be  frequent 
complaint  of  a  bad  smell.  With  normal  organs  there  may 
be  a  sensation  of  an  odor  which  cannot  be  detected  by  others 
present. 

Sneezing :  The  act  of  sneezing  is  a  violent  and  sudden  ex- 
pulsion of  air  through  the  nasal  passages.  The  act  is  a  reflex 
one  and  the  exciting  cause  is  a  stimulation  of  the  nasal  ii la- 
ments of  the  fifth  or  trifacial  nerve. 

Hearing. 

The  auditory  apparatus  consists,  in  brief,  of  (1)  the  external 
ear;  (2)  the  middle  car;  (3)  the  internal  ear;  and  (4)  the 
auditory  nerve. 


MIDDLE  EAR, 


233 


External  ear :  The  external  ear  consists  of  the  auricle  and 
external  auditory  canal.  The  former  serves  to  receive  the 
sound-waves  and  to  indicate  the  direction  from  which  they 
come  in  animals  which  possess  the  power  of  moving  the  organ. 
Through  the  external  auditory  canal  the  sound-waves  are 
conducted  to  the  middle  ear. 

The  middle  ear,  or  tympanum,  is  a  cavity  in  the  temporal 
bone  which  is  shut  off  from  the  external  auditory  canal  by 
the  membrana  tympani.  The  Eustachian  tube  connects  this 
cavity  with  the  pharynx.  The  lining  of  the  middle  ear  is 

FIG.  110. 


Right  temporal  bone  of  the  new-born  infant,  seen  from  its  inner  side,  showing  the 
membrana  tympani  and  chain  of  bones  in  their  natural  position  (Riidinger). 

partly  ciliated  epithelium,  continued  from  the  mucous  mem- 
brane of  the  pharynx  through  the  Eustachian  tube.  There 
are  two  openings  of  importance — the  fenestra  rotunda  and  the 
fenestra  ovalis — in  the  bony  wall,  but  they  are  covered,  the 
former  by  a  membrane,  the  latter  by  the  stapes.  The  middle 
ear  also  communicates  posteriorly  with  the  mastoid-cells, 
which  are  air-cavities  in  the  mastoid  process  of  the  temporal 
bone.  Its  only  communication  with  the  external  air,  how- 
ever, is  through  the  Eustachian  tube.  There  is  a  chain  of 
small  bones  (ossicles)  which  connect  the  membrana  tympani 
and  the  fenestra  ovalis. 


234 


THE  SENSES. 


Membrana  tympani :  It  is  a  tough,  tense,  fibrous  membrane 
set  in  the  bony  opening  of  the  external  auditory  canal.  The 
degree  of  tension  of  the  membrane  is  regulated  by  the  tensor 
tympani  muscle. 

Ossicles:  They  are  three  in  number  (Fig.  Ill),  and  are  so 

Fco.  ill. 


Bones  of  the  tympanum  of  the  left  side.  A,  malleus :  1,  long  or  slender  process ;  2, 
near  neck ;  3,  the  handle;  4,  short  process ;  5,  head.  B,  incus:  1,  body ;  2,  short 
or  posterior  process ;  3,  the  long  process  with  the  orbicular  process.  C,  stapes : 
1  and  2,  head ;  3,  neck  ;  4,  5,  crura;  6,  base.  D,  the  three  bones  in  their  natural 
connection  ;  TO,  malleus  ;  sc,  incus ;  «,  stapes. 

articulated  as  to  communicate  the  vibration  of  the  membrana 
tympani  to  the  internal  ear  (Fig.  110).  The  handle  of  the 
malleus  is  attached  to  the  membrane,  so  that  this  bone  moves 
with  each  vibration.  This  motion  is  communicated  to  the 
incus,  which  passes  it  on  to  the  stapes.  The  stapes  rocks  in 
the  fenestra  ovalis,  and  is  therefore  capable  of  transmitting  to 


SEMICIRCULAR   CANALS. 


235 


FIG.  112. 


the  fluid  in  the  cavity  of  the  labyrinth  the  impulses  which  it 
receives. 

Eustachian  tube :  The  Eustachian  tube  or  canal  leads  from 
the  cavity  of  the  pharynx  to  that  of  the  middle  ear.  It  is 
completely  pervious  and  allows  a  free  passage  of  air  from  the 
pharynx  to  the  middle  ear. 

Its  chief  purpose  is  to  provide  for  the  maintenance  of  an 
equal  pressure  on  both  sides  of  the  membrana  tympani,  by 
keeping  the  air  in  the  middle  ear  in  communication  with  the 
outside  air.  It  also  serves  to  render  sounds  clearer  (as  the 
apertures  in  violins  do),  and  as  an  outlet  for  mucus. 

Internal  ear  :  The  proper  organ  of  hearing  is  formed  by  the 
distribution  of  the  auditory  nerve  within  the  internal  ear  or 
bony  and  membranous  labyrinths.  The  bony  labyrinth  is  situ- 
ated in  the  dense  petrous  portion  of  the  temporal  bone,  and 
consists  of  three  essential  parts : 
the  vestibule  (Fig.  112),  and  open- 
ing from  it  the  semicircular  canals 
and  the  cochlea.  There  is  another 
opening,  the  aqueductus  vestibuli, 
whose  use  is  doubtful,  and  still 
others  for  the  entrance  of  the  audi- 
tory nerve-filaments.  Within  the 
bony  labyrinth  is  the  membranous 
labyrinth,  a  series  of  tubes  and  sacs 
composed  of  fibrous  tissue,  lined 
with  epithelium,  which  contains  a 
colorless  fluid,  the  endolymph,  while 
a  fluid  surrounds  this  membranous 
labyrinth,  the  perilymph. 

Semicircular  canals :  These  canals 
are  arched  cylindrical  spaces  in  the 
solid  bone  which  open  at  each  end 
of  the  arch  into  the  vestibule. 
They  are  three  in  number,  and  two  are  nearly  vertical  and 
one  is  horizontal.  These  canals  are  arranged  in  such  a  man- 
ner that  the  planes  of  the  two  vertical  canals  are  at  right 
angles,  one  being  antero-posterior,  and  the  other  transverse 
(Fig.  112).  These  canals  have  within  them  complete  mem- 


External  view  of  a  cast  of  the  left 
labyrinth  (Henle).  /,  fenestra 
rotunda,  or  round  window ;  a, 
fenestra  ovalis,  or  oval  window ; 
b,  ampulla  of  superior  semi- 
circular canal;  c,  ampulla  of 
horizontal  semicircular  canal; 
(1,  common  shaft  of  union  of 
these  two  canals ;  e,  ampulla 
of  posterior  semicircular  canal ; 
g,  promontory  (the  line  should 
extend  more  to  the  right). 


236 


THE  SENSES. 


branous  tubes,  considerably  smaller  than  themselves ;  so  that 
the  perilymph  occupies  the  space  between  the  bony  wall  and 
the  membranous  wall,  while  the  endolymph  occupies  the  cavity 
of  the  membranous  semicircular  canals  (Fig.  113). 

Within  the  cavity  of  the  membranous  semicircular  canals 
are  found  the  terminations  of  some  filaments  of  the  auditory 
nerve.  These  filaments  end  in  collections  of  cells  called 
"  cristae  acustica?."  A  similar  collection  of  nerve-cells,  called 
"  macula  acustica,"  is  found  in  the  membranous  chamber 

FIG.  113. 


Membranous  labyrinth.    Cs,  semicircular  canals;   U,  utriculus  ;  S,  sacculus; 
A,  aqueduct  of  vestibule;  Cr,  ductus  reunions  ;  Co,  cochlea. 

(utricle),  situated  in  the  vestibule,  into  which  the  membranous 
semicircular  canals  open. 

The  me  of  the  semicircular  canals  does  not  seem  to  be 
directly  connected  with  the  auditory  function  of  the  part,  but 
to  be  connected  more  with  the  sense  of  equilibrium.  The 
movement  of  the  fluids  in  the  canals,  arranged  in  the  direc- 
tions of  the  three  dimensions,  may  serve  to  produce  sensations 
upon  the  cristse  acusticaB  which  lead  to  the  formation  of  ac- 
curate judgment  of  changes  in  the  position  of  the  body. 

Cochlea  :  It  is  a  part  of  the  bony  labyrinth  which  derives 
its  name  from  its  resemblance  to  a  snail-shell.  It  is  divided 
into  two  parts  by  a  bony  and  membranous  septum  which 
runs  parallel  from  base  to  apex  of  the  spiral  (Fig.  114).  The 
"  upper "  passage  opens  out  of  the  vestibule,  and  is  known 
as  the  scala vestibuli ;  the  "lower,"  the  scala  tympani,  is  shut 
off  by  a  membrane,  which  covers  the  fenestra  rotunda,  from 
the  cavity  of  the  'tympanum.  The  scala  vestibuli  is  sub- 
divided by  a  membrane,  which  passes  from  the  bom  lamina 
spiralis  to  the  wall  of  the  scala  vestibuli,  shutting  off  a  tri- 


CANALIS  COCHLEARTS.  237 

angular  space  (canalis  cochlearis).     The  floor  of  this  space  is 
the  membranous   partition  (membrana  basilaris)  which  sepa- 

FIG.  114. 


Bony  cochlea  of  the  human  ear,  right  side,  opened  from  its  anterior  face 
(Cruveilhier). 

rates  the  scala  tympani  from  it,  and  upon  this  membrane  is 
the  organ  of  Corti. 

The  roof  of  the  triangular  space  is  the  membrane  of  Reissner. 

Canalis  cochlearis :  The  canalis  cochlearis,  or  scala  media, 
is  the  representative  of  the  membranous  labyrinth  occupying 
the  bony  cochlea.  It  is  a  single  continuous  tube,  spiral  in 
shape  so  as  to  conform  to  the  shape  of  the  bony  cochlea.  On 
cross-section  it  is  seen  to  be  triangular,  or,  more  correctly 
speaking,  the  segment  of  a  circle.  Its  apex  lies  just  over  the 
edge  of  the  lamina  spiralis,  and  its  base  against  the  circum- 
ference of  the  bony  cochlea.  Its  upper  side  is  the  membrane 
of  Reissner,  and  its  lower  side  the  basilar  membrane. 

At  the  apex  of  the  spiral  cochlea  the  canalis  cochlearis 
terminates  as  a  blind  end.  At  the  base  of  the  cochlea  the 
canalis  cochlearis  connects  by  means  of  a  tiny  duct  (canalis 
reuniens)  with  a  round  membranous  chamber  (the  saccule). 
The  saccule  and  utricle  are  those  portions  of  the  membranous 
labyrinth  occupying  the  bony  vestibule.  The  saccule  and 
utricle  communicate  with  each  other  by  means  of  the  "ductus 
endolymphaticus,"  a  minute  tube  lying  in  the  aqueductus 


238  THE  SENSES. 

vestibuli.  Thus  it  is  seen  that  the  canalis  cochlearis  is  filled 
with  endolymph,  freely  communicating  with  the  interior  of  the 
rest  of  the  membranous  labyrinth ;  but  nowhere  does  the 
endolymph  communicate  with  perilymph. 

Organ  of  Corti :  Upon  the  basilar  membrane  is  arranged 
a  series  of  rafter-like  bodies  which  roof  in  a  small  canal 
(Fig.  115) ;  upon  this  are  spread  the  functional  nerve-endings 
of  the  auditory  nerve.  These  rafter-like  bodies  are  large 
nucleated  cells,  the  rods  of  Corti,  having  resting  upon  them 
other  epithelial  cells  with  hair-like  processes  which  project 
into  the  canalis  cochlearis  or  scala  media.  When  looked  at 
from  above  the  cells  have  an  appearance  similar  to  the  key- 

FIG.  115. 


Diagrammatic  section  of  the  organ  of  Corti.  1,  membrana  basilaris;  2,  3,  internal 
and  external  rods  of  Corti ;  4,  epithelial  cells  near  inner  and  outer  borders ;  5, 
hair-cells  lying  in  contact  with  the  rods  (magnified  500  diameters). 

board  of  a  piano.  Fibres  of  the  auditory  nerve  spread  to 
these  cells  from  the  bony  lamina  spiralis. 

It  is  probable  that  each  of  the  functional  cells  in  the  organ 
of  Corti  responds  to  a  particular  shade  of  sound. 

Auditory  nerve :  The  Ylllth  cranial  or  auditory  nerve  is 
purely  centripetal  in  its  functions.  Anatomically  we  say 
that  its  fibres  arise  from  a  nucleus  of  gray  matter  in  the  floor 
of  the  fourth  ventricle,  and  from  this  source  pass  out  through 
the  substance  of  the  medulla  in  a  number  of  small  bundles 
which  unite  with  another  root  which  has  connections  with 
the  cerebellum  to  form  a  trunk.  This  passes  with  the  facial 
nerve  into  the  internal  auditory  canal,  and  terminates  in 
special  end-organs  in  the  internal  ear. 

Its  fibres  contain  numerous  ganglion-cells.  In  the  cochlea 
there  are  many  of  these  cells,  and  they  form  plexuses  of 
nerve-fibres  to  supply  the  hair-cells.  The  absence  of  neuri- 


COURSE  OF  SOUND-WAVES.  239 

lemma  in  the  auditory  nerve  gives  it  a  soft  feel  which  has 
caused  the  name  "  portio  mollis"  to  be  given  to  it  when  it 
and  the  facial  were  considered  as  a  single  nerve. 

Course  of  sound-waves :  Sound-waves  of  the  air  are  gath- 
ered by  the  concha,  carried  into  the  external  auditory  canal 
and  vibrate  against  the  membrana  tympani.  The  mem- 
brane taking  up  the  vibrations  transmits  them  through  the 
chain  of  ossicles  to  the  stapes  in  the  fenestra  ovalis.  The 
stapes  imparts  its  motion  to  the  perilymph  of  the  vestibule 

FIG.  116. 


„    „  „         IDTMil 

membranous  cochlea;  LS,  lamina 'ossea;  EM,  eustachian  tube ;~  AN,  auditory 
nerve  ;  N,  canalis  reuniens. 

(Fig.  116).  There  is  now  set  up  in  the  perilymph  a  fluid- 
wave  that  travels  in  all  directions.  Some  of  this  fluid-wave 
travels  along  the  scala  vcstibtili  to  the  apex  of  the  cochlea, 
then  through  the  aperture  of  communication  with  the  scala 
tympani,  then  down  the  latter  until  it  expends  itself  against 
the  membrane  in  the  fenestra  rotunda.  In  its  passage  along 
the  scala  vestibuli  and  scala  tympani,  the  fluid-wave  vibrates 
against  the  membrane  of  Reissner  and  basilar  membrane ; 
and  this  sets  up  similar  vibrations  in  the  endolymph  of 


240 


Till-:  SENSES. 


the  canalis  cochlearis.  The  fluid- wave  in  the  canalis  coch- 
learis  irritates  the  hair-cells  of  the  organ  of  Corti.  These 
cells  seem  to  be  able  to  respond  to  particular  tones  by  their 
sensitiveness  in  selecting  each  one  its  particular  fluid-wave 
with  its  particular  rate  of  vibration. 

The  remainder  of  the  fluid-wave  is  expended  in  a  similar 
manner  through  the  vestibule  and  semicircular  canals,  with 
similar  effects  on  the  saccule,  utricle,  and  membranous 
canals. 

Localization  of  hearing :  The  branch  of  the  eighth  nerve, 
"  arising"  in  the  organ  of  Corti,  having  received  its  impulses 
from  the  organ  of  Corti  cells,  transmits  its  impulse  to  the 

FIG.  117. 


Position  of  the  auditory  centre  in  the  first  temporal  convolution  (Gowers). 

centre  under  the  acoustic  tubercle  in  the  floor  of  the  fourth 
ventricle;  thence  fibres  pass  by  means  of  the  trapezium  (in 
the  pons)  to  the  opposite  side,  and  thence  through  the  lower 
fillet  of  that  side  to  the  posterior  quadrigeminal  body,  whence, 
by  means  of  its  brachium,  internal  geniculate  body,  optic 
thalamus,  and  internal  capsule,  they  proceed  to  the  cortex 
of  the  first  and  second  temporal  convolutions  (Fig.  117). 

Distance:  We  can  only  judge  of  the  distance  of  the  source 
of  a  sound  by  its  intensity.  The  sound  itself  is  in  the  ear. 
Ventriloquists  take  advantage  of  this  fact,  and,  by  modify- 
ing the  intensity  of  the  voice  in  imitation  of  the  effect  of 
distance,  cause  us  to  think  that  it  really  originates  at  a 
distance. 

Subjective  hearing :  By  this  heading  is  meant  those  sounds 


PRODUCTION   OF   VOICE.  241 

that  are  distinctly  heard  and  yet  are  not  produced  by  phys- 
ical sound-waves,  nor  are  they  hallucinations.  They  may  be 
due  to  disturbances  of  the  auditory  apparatus  or  to  abnormal 
conditions  of  surrounding  organs.  Thus,  buzzing  or  ringing 
in  the  ears  may  result  from  the  hypersemia  of  the  parts  and 
exaggerated  rush  of  blood,  or  from  a  defect  in  the  circulating 
apparatus  (as  by  an  aneurism),  or  from  disease  in  the  auditory 
nerve  or  some  other  portion  of  the  apparatus.  Hallucina- 
tions of  hearing  are  very  common  among  the  insane,  and  are 
purely  creations  of  the  disordered  brain. 

Musical  range  of  hearing  :  The  range  of  musical  notes  that 
can  be  appreciated  by  the  human  ear  is  about  seven  octaves. 
There  are  about  three  thousand  hair-cells  in  the  organ  of 
Corti,  and  it  will  be  easily  seen  that  this  would  allow  an 
enormous  capability  to  differentiate  sounds  and  musical  tones. 
This  corresponds  to  a  range  of  from  40  to  about  4000  vibra- 
tions per  second.  The  range  of  audibility,  on  the  other  hand, 
is  about  eleven  octaves,  or  from  16  to  38,000  vibrations  per 
second.  With  less  than  16  vibrations  per  second  we  are 
conscious  only  of  separate  shocks,  while  with  more  than  the 
larger  number  we  are  unconscious  of  sound  altogether. 

Voice  or  Speech. 

Although  the  voice  or  speech  cannot  be  called  part  of  the 
senses,  nevertheless  it  seems  appropriate  to  describe  its  mechan- 
ism under  the  general  subject  of  "  The  Senses." 

The  larynx :  The  larynx  is  the  organ  of  voice.  It  is  a 
cavity  closed  laterally,  but  communicating  with  the  trachea 
below  and  the  pharynx  above.  The  walls  are  made  up  of 
the  thyroid,  cricoid,  and  arytenoid  cartilages,  together  with 
various  muscles  and  membranes  (Fig.  118).  For  a  detailed 
description  see  Quain's  or  Gray's  Anatomy. 

Across  the  cavity  of  the  chamber  are  stretched  in  an 
antero-posterior  direction  the  two  vocal  cords  or  "  mem- 
branes." The  free  passage  between  the  vocal  cords  is  the 
glottis,  the  cords  forming  part  of  the  rima  glottidis. 

Production  of  voice :  Voice  is  a  result  of  the  vibrations 
of  the  vocal  cords.  The  vibration  of  the  vocal  cords  is 

16— Phys. 


242 


THE  SENSES. 


produced  by  the  passage  of  the  air  in  expiration,  never 

naturally  in  inspiration.  The 
I'I<;-  118-  quality  of  the  voice  as  regards 

pitch  depends  upon  the  length 
of  the  vocal  cords,  the  crico- 
thyroid  muscles  acting  to  in- 
crease the  tension,  while  the 
thyro-arytenoids  relax  the 
cords  and  the  crico-arytenoids 
dilate  and  contract  the  rim  a 
glottidis.  Falsetto  and  high- 
pitched  notes  in  a  naturally 
low-pitched  voice  are  due  to 
vibration  at  the  edges  of  the 
cords.  The  hollow  spaces 
about  the  oral  and  nasal  cav- 
ities are  of  use  as  resonators 
or  sounding-boards. 

Articulate  speech  :  The  voice 
comes  from  the  larynx  ;  but 
articulate  speech  is  the  result 
of  the  modification  of  the 
voice  by  the  tongue,  etc. 
(Fig.  119). 

The  organs  used  in  articu- 
late speech  are  :  The  tongue 
and  teeth  in  the  formation  of 
the  linguals  and  dentals  ;  the 
nasal  sounds  by  the  cavity 
of  the  nose  ;  the  other  sounds 
are  formed  largely  by  modi- 
fications in  the  shape  of  the 
mouth  in  one  or  another  part. 

Musical  range  of  the  voice : 
The  musical  range  of  a  hu- 
man voice  is  from  one  to 
three  octaves.  In  this,  culti- 
vation and  natural  aptitude 
are  factors  which  permit  great  variability.  The  total  range 


Longitudinal  section  of  the  human 
larynx,  showing  the  vocal  mem- 
branes. 1,  ventricle  of  the  larynx  ;  2, 
superior  vocal  membrane  ;  3,  inferior 
vocal  membrane ;  4,  arytenoid  car- 
tilage ;  5,  section  of  the  arytenoid 
muscle;  6,  6,  inferior  portion  of  the 
cavity  of  the  larynx  ;  7,  section  of 
the  posterior  portion  of  the  cricoid 
cartilage ;  8.  section  of  the  anterior 
portion  of  the  cricoid  cartilage :  9, 
superior  border  of  the  cricoid  cartil- 
age ;  10,  section  of  the  thyroid  car- 
tila-c  :  11,  11,  superior  portion  of  the 
cavity  of  the  larynx ;  12, 13,  aryten- 
oid gland;  14,  16,  epiglottis;  15,  17, 
adipose  tissue;  18,  section  of  the 
hyoid  bone ;  19, 19, 20,  trachea. 


EYELIDS. 


243 


of  the  human  voice  from  the  highest  soprano  to  the  lowest 
bass  is  about  four  octaves.     Thus  it  will  be  seen  that  the 


Section  of  the  parts  concerned  in  the  formation  of  vowels.  Z,  tongue  ;  p,  soft  pal- 
ate ;  e,  epiglottis ;  g,  glottis  ;  h,  hyoid  bone ;  1,  thyroid  :  2, 3,  cricoid ;  4,  arytenoid 
cartilage  (Landois). 

range  of  sounds  which  can  be  appreciated  by  the  ear  is  far 
beyond  the  capacity  of  the  voice. 

Sight. 

The  visual  apparatus  is  the  eye  with  its  accessory  organs 
and  the  optic  nerve. 

The  function  of  the  eye  is  the  reception  of  stimuli  of  light, 
whereby  we  are  able  to  perceive  the  impressions  of  form, 
color,  and  conditions  of  our  surroundings  in  infinite  variety. 
It  is  far  the  most  complex  in  structure  of  any  of  the  organs 
of  special  sense,  and  the  most  rapid  and  delicate  in  its  actions. 
The  stimulus  received  by  the  eye  is  transmitted  along  the 
optic  nerve  to  the  brain. 

Accessory  organs  of  the  eye  :  Under  this  heading  we  class  the 
(1)  eyelids,  (2)  lachrymal  gland,  (3)  extrinsic  muscles  of  the 
eyeball. 

Eyelids :  Each  eye  has  two  lids,  an  upper  and  a  lower.  Each 
consists  of  a  thin  plate  of  elastic  tissue  with  a  covering  of 
loose  skin  and  a  smooth  lining  of  mucous  membrane — the 
conjunctiva — which  is  reflected  upon  the  eyeball.  Along  the 


244  THE  SENSES. 

edges  of  the  lids  are  a  number  of  short  curved  hairs  which 
screen  the  eye  from  foreign  bodies.  The  extreme  sensitive- 
ness of  the  conjunctiva  helps  in  this  by  giving  immediate 
warning  when  any  foreign  substance  gets  in  the  eye. 

The  muscles  of  the  eyelids  are  the  levator  palpebrse  supe- 
riores  and  the  orbicularis  palpebrarum. 

Lachrymal  gland :  It  is  a  small  racemose  gland  lodged  in 
the  upper  and  outer  part  of  the  orbit.  It  has  several  ducts, 
which  lead  to  the  surface  of  the  conjunctiva  of  the  upper  lid. 
The  secretion  of  the  gland  is  usually  just  sufficient  to  keep  the 
eye  moist,  but  under  the  stimulus  of  pain  or  intense  emotion  the 
secretion  is  increased,  and  appears  in  drops  which  flow  from 
the  eyes — tears.  Under  ordinary  circumstances  a  slight  ex- 
cess of  this  moisture  is  drained  into  the  nasal  cavity  by  the 
lachrymal  duct.  This  secretion  is  slightly  alkaline,  and  con- 
tains about  1  per  cent,  of  solids,  chiefly  sodium  chloride. 

Meibomian  glands :  They  consist  of  a  number  of  small 
racemose  glands,  lying  beneath  the  conjunctiva,  which  secrete 
an  oily  protective  substance.  The  ducts  of  these  glands  open 
along  the  edge  of  the  lid. 

Extrinsic  muscles  of  the  eye  :  There  are  six  muscles  to  each 
eye — superior  rectus,  external  rectus,  inferior  rectus,  internal 
rectus — situated  respectively  above,  below,  and  to  the  inner,  and 
outer  sides  of  the  eyeball ;  also  the  superior  oblique  at  the 
upper  and  inner  angle  of  the  orbit,  and  the  inferior  oblique 
at  the  lower  and  inner  angle. 

The  recti  serve  to  turn  the  eye  up,  down,  in,  or  out,  accord- 
ing to  which  muscles  or  combination  of  muscles  are  acting. 
The  oblique  muscles  tend  to  rotate  the  eyeball  on  an  antero- 
posterior  axis. 

The  superior  and  inferior  recti  of  both  eyes  work  synchro- 
nously, but  the  action  of  the  external  rectus  of  one  eye  is 
synchronous  with  the  internal  rectus  of  the  other;  and  the 


same  is  true  as  between  the  superior  oblique  of  one  eye  ;m<l 

ique  of  the  other.     The  objec 
of  all  these  muscles  is  to  turn  the  eyeballs  toward  the  object 


the  inferior  oblique  of  the  other.     The  object  of  the  action 


to  be  seen,  thus  causing  it  to  receive  the  majority  of  the  rays 
from  the  object  at  right  angles  to  the  surface  of  the  eye.  The 
superior  oblique  muscles  are  supplied  by  the  fourth  cranial 


COATS  OF  THE  EYEBALL. 


245 


nerves  ;  external  recti  by  the  sixth  ;  the  other  muscles  by  the 
third  cranial  nerves. 

The  eyeball  consists  of  a  tough,  opaque  globe  (Fig.  120), 
having  a  somewhat  more  sharply-curved  translucent  portion, 
the  cornea,  at  the  front.  It  has  in  the  anterior  portion  a  lens, 
and  in  front  and  behind  this  are  chambers  which  contain 


FIG.  120. 


Horizontal  section  of  the  right  eyeball.  1,  optic  nerve;  2,  sclerotic  coat:  3,  cornea; 
4,  canal  of  Schlemm  ;  5,  choroid  coat ;  6,  ciliary  muscle ;  7,  iris ;  8,  crystalline 
lens ;  9,  retina ;  10,  hyaloid  membrane ;  11,  canal  of  Petit ;  12,  vitreous  body. 

fluids  :  the  one  in  front  is  the  anterior  chamber,  and  contains 
the  aqueous  fluid,  while  in  the  posterior  is  the  vitreous  humor. 
These  structures  fill  the  eyeball  and  give  it  a  tense  feel  to 
the  touch. 

Coats  of  the  eyeball:  The  anterior  portion  of  the  eye, 
which  has  already  been  described  as  being  more  sharply 
curved  than  the  rest,  is  the  cornea.  If  we  examine  the  rest 
of  the  eyeball  (Fig.  121),  it  will  be  found  to  consist  of  three 


246  THE  SENSES. 

coats  :  (1)  The  sclera,  or  sclerotic  coat,  is  external,  and  covers 
about  five-sixths  of  the  globe.  The  cornea  is  continuous  with 
it  in  front.  It  is  composed  of  tough  white  fibres  arranged  in 
intercommunicating  layers.  (2)  The  choroid  coat  is  very 
vascular,  being  composed  of  a  mesh  of  capillaries.  There  is 
outside  of  this  a  layer  of  connective  tissue  containing  pigmeut- 

FIG.  121. 


Choroid  membrane  and  iris  exposed  by  the  removal  of  the  sclerotic  and  cornea. 
Twice  the  natural  size,  rf,  one  of  the  segments  of  the  sclerotic  thrown  back; 
I  and  k,  iris ;  c,  ciliary  nerves ;  e,  one  of  the  vasa  vorticosa  or  choroidal  veins 
(Quain).  The  ciliary  muscle  is  crossed  by  the  line  from  k,  and  should  be  repre- 
sented as  radiating. 

granules,  so  that  the  choroid  is  black.  (3)  The  retina,  which 
is  the  seat  of  the  end-organs  of  the  optic  nerve. 

The  purpose  of  the  sclera  is  solely  to  act  as  a  capsule  for 
.the  contents  of  the  eye.  The  choroid  being  black  prevents 
any  reflection  of  light.  The  retina  is  the  nervous  organ  for 
receiving  the  sensations. 

The  cornea  is  continuous  with  the  sclera  in  the  front  of  the 
eye,  and  occupies  about  one-sixth  of  the  surface  (3,  Fig.  120). 
Its  shape  is  that  of  a  small  dome  set  upon  the  globe  of  the 
eye.  It  has  in  front  several  layers  of  epithelial  cells,  and  at 


CILIARY  MUSCLE.  247 

the  posterior  surface  a  thin  epithelial  lining  (membrane  of 
Descemet) ;  but  the  main  body  of  the  structure  consists  of 
interlacing  connective-tissue  fibres,  which  have  spaces  in 
which  are  found  branching  cells  peculiar  to  the  structure. 
The  cornea  is  perfectly  transparent  ;  it  has  no  bloodvessels. 

The  aqueous  humor  is  a  watery  fluid  contained  in  the  ante- 
rior chamber.  It  acts  with  the  cornea  as  a  refracting  medium 
to  concentrate  rays  of  light  upon  the  lens,  to  maintain  the 
globular  form  of  the  cornea,  and  to  float  the  iris  and  allow  it 
freedom  of  motion. 

The  indices  of  refraction  for  cornea  and  aqueous  humor  are 
about  the  same ;  so,  as  far  as  being  media  of  refraction,  we 
consider  the  cornea  and  aqueous  humor  as  one,  with  an  index 
of  refraction  of  1.33. 

The  crystalline  lens  is  a  double  convex  lens  (8,  Fig.  120) 
of  high  refractive  power  which  is  suspended  in  the  anterior 
portion  of  the  eye  immediately  behind  the  anterior  chamber. 
Its  function  is  to  bring  the  rays  of  light  to  a  focus  upon  the 
retina.  In  structure  the  lens  is  composed  of  concentric  layers 
of  long,  slender  fibres  enclosed  in  a  thin  capsule.  The  index 
of  refraction  for  the  crystalline  lens  is  about  1.45.  The  crys- 
talline lens  is  suspended  in  its  capsule  by  the  suspensory  lig- 
ament, and  this  is  controlled  by  the  ciliary  muscle.  At  rest 
the  eye  is  focussed  for  seeing  at  a  distance,  and  the  lens  is  held 
somewhat  flattened  by  the  tension  of  the  suspensory  ligament. 
When  focussing  upon  a  near  object  the  ciliary  muscle  contracts, 
and  the  lens  is  permitted  to  project  more  as  the  tension  of  the 
ligament  relaxes. 

The  ciliary  muscle  extends  as  a  narrow  zone  of  muscle- 
fibres  near  the  anterior  part  of  the  choroid.  The  muscle- 
fibres  originate  at  about  the  junction  of  the  cornea  and  sclera 
and  pass  backward  meridianally  to  be  inserted  in  the  choroid 
coat.  On  contraction  the  ciliary  muscles  draw  the  choroid 
coat  forward  ;  this  relaxes  the  suspensory  ligament  of  the  lens 
and  the  lens  becomes  more  convex. 

When  the  ciliary  muscle  relaxes  the  reverse  takes  place, 
the  choroid  being  replaced  by  the  natural  tension  of  the  con- 
tents of  the  eye.  The  nerves  to  the  ciliary  muscle  are  from 
the  ciliary  ganglion. 


248  THE  SPJNSES. 

The  iris  is  a  curtain  of  muscular  tissue  placed  vertically  in 
front  of  the  lens.  The  fibres  of  the  muscular  tissue  are  both 
circular  and  radiating,  so  that  they  serve  to  decrease  and  in- 
crease the  size  of  the  pupil  as  one  or  the  other  set  of  fibres 
acts.  It  has  a  pigment-layer  upon  the  inner  surface,  which 
is  continued  from  the  choroid,  and  upon  the  amount  of  the 
coloring-matter  depends  the  "  color  of  the  eyes." 

In  the  centre  of  the  iris  is  a  circular  opening,  through 
which  light  enters  the  "dark-chamber"  of  the  eye.  This 
opening  is  the  pupil. 

Nervous  control  of  the  iris  :  Contraction  or  dilatation  of  the 
pupil  is  a  reflex  act,  and  the  afferent  stimulus  is  carried 
through  the  optic  nerve  and  the  motor  through  the  third 
cranial  nerve,  acting  from  a  centre  just  beneath  the  aqueduct 
of  Sylvius  and  the  corpora  quadrigemina.  The  increase  in 
the  amount  of  light  which  reaches  the  retina  causes  a  con- 
traction of  the  pupil,  and  a  decrease  is  followed  by  dilatation. 
Aside  from  this,  the  needs  of  the  eye  regulate  the  amount  of 
light ;  thus,  for  near  work  the  pupil  contracts,  and  dilates 
when  the  eye  is  focussed  upon  a  distant  objec.t. 

The  pupil  is  controlled  also  through  the  sympathetic  and 
the  fifth  nerve,  through  the  connection  of  the  third  and  fifth 
nerves  with  the  ciliary  ganglion  of  the  sympathetic  system. 
Drugs  are  active  also,  both  locally  and  internally,  in  control- 
ling the  action  of  the  iris  without  reference  to  the  reflex 
fibres  :  atropine  both  locally  and  internally  dilates  the  pupil ; 
opium  internally,  and  eserine  locally  contract  it. 

Vitreous  humor  :  The  vitreous  body  (or  humor)  is  a  semifluid 
gelatinous  substance  which  fills  the  posterior  chamber  and 
constitutes  about  four-fifths  of  the  bulk  of  the  eye.  It  is 
quite  transparent,  and  acts  to  maintain  the  tension  of  the  eye- 
ball, and  as  a  refracting  medium  through  which  light  reaches 
the  retina. 

Refraction :  In  order  clearly  to  understand  the  nature  of  the 
image  received  by  the  eye,  it  will  be  wise  to  review  the  im- 
ages cast  by  a  convex  lens.  If  we  take,  for  example,  a  double 
convex  lens  and  note  the  image  formed  by  a  luminous  object, 
we  see  that  it  is  an  inverted  image  at  the  point  of  focus  of 
the  lens  if  the  luminous  object  is  placed  at  a  distance  (Fig. 


REFRACTION  IN  THE  EYE.  249 

122).  Referring  to  this  figure,  it  will  be  seen  that  the  rays 
originating  at  A  will  be  twice  refracted,  once  by  the  lens  and 
again  in  leaving  it,  so  that  all  rays  from  A  reaching  the  lens 
are  joined  at  a.  The  same  is  true  for  B  and  6.  Therefore  a 


FIG.  122. 


Formation  of  image  by  convex  lens. 

screen  placed  at  the  focus,  F,  will  receive  an  inverted  image, 
a  6,  of  the  luminous  object,  A  B. 

If  the  lens  were  more  convex,  the  image  would  be  formed 
nearer  the  lens ;  if  the  lens  were  flatter,  the  image  would  be 
further  from  the  lens. 

Again,  on  the  other  hand,  if  we  decide  to  have  the  image 
formed  at  a  definite  spot,  the  further  the  object  is  from  the 
lens  the  flatter  the  lens  must  be,  and  vice  versa,  the  nearer 
the  object  the  more  curved  the  lens  must  be. 

Thus,  with  a  double  convex  lens  we  see  that  the  image 
formed  is  a  real,  inverted  image  on  the  opposite  side  of  the 
lens  from  the  object. 

Refraction  in  the  eye :  The  crystalline  lens  is  a  double 
convex  lens  and  so  obeys  the  laws  referred  to  in  the  previous 
paragraph. 

In  addition  to  the  crystalline  lens  the  other  refracting 
media  (Fig.  123)  of  the  eye  are  the  cornea,  aqueous  and 
vitreous  humors.  The  tendency  of  all  these  refracting  media 
is  to  bring  together  to  one  focus  all  divergent  rays  of  light ; 
thus  they  may  be  considered  as  a  group  of  double  convex 
lenses.  The  crystalline  lens,  however,  is  the  most  important, 
as  it  possesses  the  power,  by  virtue  of  the  ciliary  muscles, 
of  increasing  or  diminishing  its  curvature. 


250 


THE  SENSES. 


B,  a  candle  placed  at  the  side  of 
the  eye— that  is.  as  much  to  the 
side  of  the  centre  of  the  cornea 
as  possible.  B',  interior  luminous 
source,  formed  by  the  rays  of 
light  concentrated  by  the  crys- 
talline lens  upon  the  extreme 
lateral  portion  of  the  eye.  CD, 
two  vessels  of  the  retina  (the  size 
of  the  retina  is  here  greatly  ex- 
aggerated). The  shadow  of  these 
two  vessels  is  seen  as  if  projected 
at  D'  and  C •'.  Experiment  by 
Purkinje. 


Accommodation:   By  accommodation  we  mean  the  power 

of  the  crystalline  lens  to  change 
its  amount  of  curvature  so  as  to 
throw  the  image  of  an  object  in 
exact  focus  on  a  fixed  screen  (the 
retina)  whether  the  object  be 
near  or  far  from  the  lens.  At 
the  same  time  the  pupil  is  ex- 
panded or  contracted  to  admit 
the  necessary  amount  of  light. 
Thus,  if  an  object  be  near  the 
eye,  in  order  to  produce  a  sharp 
image  the  lens  is  more  curved, 
owing  to  contraction  of  the  cil- 
iary muscle,  and  the  pupil  is  con- 
tracted. If,  on  the  other  hand, 
the  object  be  on  the  horizon,  the 
ciliary  muscle  relaxes,  the  lens  is 
flatter,  and  the  pupil  is  dilated. 
Comparison  of  eye  to  photographic  camera :  The  eye  may  be 
compared  to  the  photographic  camera.  It  contains  various 
media  for  the  refraction  of  light,  and  a  screen  at  the  back  for 
receiving  the  image.  The  refracting  media  are  the  cornea, 
aqueous  humor,  crystalline  lens,  and  the  vitreous  humor : 
the  screen  is  the  retina.  The  pigment  of  the  retina  and 
choroid  makes  the  interior  dark,  a  necessary  feature  in  such 
an  apparatus.  The  mechanism  of  the  lens  enables  the  eye  to 
be  focussed  for  distance,  while  the  iris  regulates  the  proper 
admission  of  light. 

In  a  camera  the  ground-glass  screen,  or  the  sensitive  plate, 
is  moved  nearer  or  further  from  the  back  of  the  lens  in  order 
to  bring  it  in  focus — i.  e.,  make  the  image  clear.  In  the  eye 
the  sensitive  plate  (the  retina)  is  at  a  fixed  distance  from  the 
lens,  and  so  the  focussing  is  done  by  a  change  in  the  curvature 
of  the  lens  (accommodation). 

The  retina  is  comparable  to  the  photographic  sensitive 
plate.  It  receives  the  images  formed  upon  it  by  the  lens  and 
transmits  the  impressions  to  the  optic  nerve,  whence  they  are 
carried  to  the  brain. 


RODS  AND   CONES. 


251 


FIG.  124. 


It  will  be  remembered  that  the  retina  forms  the  most  cen- 
tral of  the  layers  of  the  eyeball,  but  does  not  extend  as  far 
forward  as  do  the  choroid  and  sclera,  but  terminates  at  about 
half  way. 

The  fibres  of  the  optic  nerve,  after  piercing  the  sclera  and 
choroid  at  the  back  of  the  eye,  spread  out  divested  of  neuri- 
lemma  and  medullary  sheath  into  the  innermost  layer  of  the 
retina.  The  fibres  then  pass,  with  more  or  less  direct  com- 
munications, peripherally  through  the  other  layers  until  they 
may  be  said  to  terminate  in  the 
layers  of  rods  and  cones,  exter- 
nal to  which  is  a  pigment-layer. 

Rods  and  cones  :  They  are 
closely  packed  on  the  outer  sur- 
face of  the  retina,  the  rods  be- 
ing the  more  numerous  in  most 
situations.  The  cones  seem  to 
be  modifications  of  the  rods,  and 
their  office  is  essentially  sim- 
ilar. The  rods  (Fig.  124)  are 
straight  cylindrical  bodies  of  a 
transparent  substance,  and  are 
placed  parallel  to  one  another  and 
perpendicular  to  the  surface  of 
the  eyeball.  In  length  they  are 
about  five  to  seven  times  the  di- 
ameter of  a  red  blood-corpuscle, 
and  in  diameter  about  one-twen- 
tieth of  their  length.  The  cones 
are  very  similar,  except  that  their 
conical  shape  makes  them  appear 
to  be  of  different  character.  The 
cones  do  not  always  reach  to  the 
same  level  as  the  rods.  When 

viewed  from  the  peripheral  SUr- 
f  .1  j  />  ,1  j  j 

tace     the    ends    Ol     the     rods     and 

cones  give  the  appearance  of  a 
fine  mosaic.  These  organs  are 
connected  with  the  subjacent  layers,  and,  ultimately,  more  or 


Diagrammatic  section  from  the 
posterior  portion  of  the  human 
retina.  1,  layer  of  rods  and 

layer    °f    nuclei 


252  THE  SENSES. 

less  directly,  with  the  axis-cylinders  of  the  fibres  of  the  optic 
nerve. 

The  optic  nerve  pierces  the  eyeball  not  exactly  at  its  most 
posterior  point,  but  a  little  to  the  inner  side.  At  the  exact 
centre  of  the  retina — that  is,  the  most  posterior  point  of  the 
eye — there  is  a  small  yellow  area  (macula  luted)  with  a  cen- 
tral depression  (fovea  central-is).  Here  are  found  none  of  the 
fibres  of  the  optic  nerve,  but  a  great  increase  in  the  numbers 
of  the  cones ,  as  well  as  an  increase  in  their  size. 

Area  of  most  acute  vision  :  If  the  object  looked  at  is  focussed 
directly  upon  the  macula  lutea,  the  image  is  then  seen  with 
the  greatest  clearness.  This  is  to  be  expected,  for  in  the 
macula  lutea  we  find  the  end-organs  of  the  optic  nerve  most 
highly  developed.  In  every-day  life  we  look  directly  at  an 
object  so  as  to  receive  the  image  on  the  macula  lutea  and 
thus  render  the  perception  more  acute.  Rays  of  light  enter- 
ing the  eye  on  an  angle  are  focussed  on  some  other  part  of 
the  retina  and  are  not  so  clearly  defined. 

Blind  spot :  If  the  left  eye  is  covered  and  the  right  directed 
steadily  upon  the  cross  in  Fig.  125,  the  circular  spot  will  be 

FIG.  125. 


visible  at  the  same  time,  though  less  distinctly.  As  the  book 
is  moved  slowly  backward  and  forward,  a  point  will  be  found 
at  which  the  round  spot  disappears,  reappearing  as  the  book 
is  held  nearer  or  farther  or  as  it  is  inclined  in  cither  direction 
and  the  image  is  carried  away  from  the  "blind  spot." 

The  blind  spot  is  the  point  where  the  optic  nerve  enters 
the  eye.  If  the  image  be  focussed  on  this  point  no  perception 
follows,  as  that  part  of  the  retina  is  deficient  in  rods  and 
cones  (Fig.  126). 


FIBRES  OF  NERVES  AND   TRACTS.  253 

FIG.  126. 


The  posterior  half  of  the  retina  of  the  left  eye  viewed  from  before.  Twice  its 
natural  size,  s,  cut  edge  of  the  sclerotic ;  ch,  chproid ;  r,  retina :  in  the  interior 
at  the  middle  the  macula  lutea  with  the  depression  of  the  fovea  centralis  is  rep- 
resented by  a  slight  oval  shade  :  toward  the  left  side  the  light  spot  indicates  the 
colliculus  or  eminence  at  the  entrance  of  the  optic  nerve,  from  the  centre  of 
which  the  arteria  centralis  is  seen  sending  its  branches  into  the  retina,  leaving 
the  part  occupied  by  the  macula  entirely  free  (Henle). 

Optic  nerve :  If  one  examines  the  optic  nerves  in  a  super- 
ficial manner,  they  will  be  seen  to  leave  the  back  of  each  eye, 
passing  backward  through  the  optic  foramina  until  they 
reach  the  body  of  the  sphenoids.  Here  the  optic  nerves 
cross  one  another  in  the  form  of  an  X  (the  optic  chiasm),  the 
fibres  intermingling,  and  the  right  nerve  apparently  passing 
over  to  the  left  side  and  the  left  nerve  to  the  right  side. 
The  posterior  limbs  of  the  X  pass  backward  and  are  called 
the  optic  tracts.  The  optic  tracts  in  their  backward  course 
curve  around  the  crura  cerebri  to  terminate  in  the  ganglion- 
cells  of  the  pulvinar,  anterior  quadrigemina,  and  external 
geniculate  bodies.  From  the  ganglion-cells  of  the  pulvinar, 
anterior  quadrigemina  and  external  geniculate  bodies,  fibres, 
called  the  optic  radiations,  pass  backward  to  terminate  in  the 
ganglion-cells  of  the  cortex  of  the  posterior  part  of  the  occip- 
ital lobes. 

Fibres  of  nerves  and  tracts :  A  more  minute  examination 
of  the  optic  nerves  will  show  that  each  optic  nerve  consists 
of  two  distinct  bundles  of  fibres  laterally  placed.  The  inner 


254 


THE  SENSES. 


set  of  fibres  being  the  fibres  from  the  inner  half  of  the  retina ; 
the  outer  bundle  of  fibres  coming  from  the  outer  half  of  the 
retina.  If  we  trace  these  bundles  backward  to  the  optic 


FIG.  127. 


Left  Eye 


Right  Eye 


Optic 


ic  nerve 


Optic  radiation 


Optic  radiation 


rlc'x  of  occipital 
lobe  with  cortical  cells 


1,  external  geniculate  body;  2,  pulvinar;  3,  anterior  quadrigeminate  body;  4,  in- 
ternal genioulate  body ;  5,  commissure  of  (Judden. 

chiasm,  it  is  noted  that  only  the  inner  bundles  decussate 
and  pass  to  the  opposite  side  of  the  brain.  The  external 
bundles  do  not  decussate,  but  pass  directly  backward  as  part 


BINOCULAR    VISION.  255 

of  the  optic  tracts  to  terminate  in  the  ganglia  on  their  respec- 
tive sides  of  the  brain. 

Thus  the  left  pulvinar,  left  anterior  quadrigeminate  and 
external  geniculate  bodies  receive  the  fibres  from  the  inner 
half  of  the  right  eye  and  the  outer  half  of  the  left  eye.  The 
right  ganglia  receive  fibres  from  the  inner  half  of  the  left  eye 
and  outer  half  of  the  right  eye. 

Commissure  of  Gudden :  There  is  also  in  the  optic  tracts  a 
bundle  of  fibres  arising  from  the  internal  geniculate  body  of 
one  side,  passing  forward,  as  a  third  and  innermost  bundle 
of  the  optic  tracts,  to  the  back  part  of  the  optic  chiasm  ;  here 
the  fibres  bend  on  themselves  and  pass  backward  along  the 
inner  margin  of  the  opposite  optic  tract  to  terminate  in  the 
other  internal  geniculate  body.  These  commissure!  fibres 
form  the  commissure  of  Gudden,  and  serve  to  connect  the  two 
internal  geniculate  bodies.  They  play  no  part  in  vision. 

Nervous  mechanism  of  vision :  The  image,  properly  re- 
ceived on  the  retina,  stirs  the  rods  and  cones  into  functional 
activity.  The  u  vibrations  "  are  then  passed  along  the  optic 
nerves  and  optic  tracts  to  terminate  in  the  pulvinares,  exter- 
nal geniculate  and  anterior  quadrigeminate  bodies.  These 
structures  may  be  called  the  primary  vision  centres.  Here 
the  impressions  of  sight  are  received  in  a  physical  sense,  but 
the  mind  does  not  as  yet  appreciate  the  sight  impression. 

The  impression  received  by  the  ganglia  are  now  trans- 
mitted along  the  optic  radiations  to  the  cortical  cells  of  the 
occipital  lobes.  When  the  cortical  cells  are  stimulated  the 
mind  is  capable  of  appreciating  that  " we  see"  So  we  may 
call  the  ganglia  the  seat  of  physical  sight,  but  the  cortical 
cells  are  the  seat  of  physiological  sight. 

Binocular  vision :  In  normal  vision  both  eyes  are  used,  so 
that  a  separate  image  is  received  on  each  retina.  Through 
the  intimate  association  of  the  two  halves  of  the  brain  we  are 
conscious  of  but  one  image. 

A  further  advantage  of  binocular  vision  is  that  each  eye 
looking  at  an  object  from  a  slightly  different  standpoint  sees 
a  little  more  on  one  side  or  other  of  the  object  than  does  the 
other  eye.  Thus  the  combined  image  formed  contains  a  little 
more  of  the  object  than  would  the  image  from  one  eye  alone. 


256 


Till':  SENSES. 


Thus  the  perceptive  faculties  can  judge  more  correctly  of  the 
form  and  diddnce  of  an  object. 

The  stereoscope  illustrates  this  point.  In  this  instrument 
two  photographs  are  taken  by  cameras  so  placed  as  to  repre- 
sent the  position  of  the  eyes  in  vision,  and  the  two  views  of 
one  object  are  then  superimposed  by  the  use  of  prisms  (Fig. 
128). 

Photographic  views  seen  through  a  stereoscope  possess  a 
rounded-out,  lifelike  appearance  not  seen  in  ordinary  photo- 
graphs. 

Inversion  of  the  image  :  From  the  laws  of  optics  we  know 
that  the  image  formed  on  the  retina  is  an  inverted  image  of 

FIG.  128. 


Illustrating  the  principle  of  the  stereoscope  and  binocular  vision. 

the  object.  Yet  we  perceive  the  object  in  its  upright  posi- 
tion. This  is  the  result  of  lifelong  habit.  A  baby  sees  an 
object;  the  next  step  is  to  touch  it;  by  practice  the  child 
finds  out  which  is  the  top  of  the  object  through  the  touch- 
perception.  He  then  corrects  his  mental  impression.  Very 
speedily  the  brain  learns  to  make  the  correction,  and  the  les- 
son once  learned  lasts  through  life. 

The  correction  is  made  by  the  brain  in  its  perception  of  the 
image.  It  is  an  act  of  mental  and  not  of  physical  origin. 
Tims,  objects  which  are  projected  upon  the  left  of  the  retinal 
surface  look  to  be,  as  they  are,  on  the  right  of  the  body  ;  and 
so  with  all  the  directions :  the  inversion  of  the  retinal  image 
is  corrected  by  the  mind. 

Duration  of  visual  sensations:  The  duration  of  a  visual  sen- 
sation is  always  greater  than  that  of  the  stimulus  which  has 
caused  it.  However  brief  the  luminous  impression,  the  effect 
on  the  retina  lasts  about  one-eighth  of  a  second.  The  spokes 


RETINAL   RED.  257 

of  a  rapidly  revolving  wheel  for  this  reason  do  no  not  appear 
as  spokes,  but  as  a  solid  mass,  each  following  one  another  so 
rapidly  that  one  impression  cannot  fade  away  before  another 
lias  replaced  it. 

Mental  processes  acting  on  visual  perceptions  :  We  are  able  to 
estimate  by  the  aid  of  the  brain  the  size,  direction,  distance, 
form,  and  speed  of  motion  of  a  thing  which  we  have  seen. 
All  of  these  are  judgments  based  largely  upon  previous  ex- 
perience. All  of  these  deductions  are  liable  to  error  by  rea- 
son of  faulty  judgment  or  faulty  vision,  but  this  is  the  usual 
method  of  forming  such  estimates.  As  an  example  of  visual 
illusion,  the  two  centre  squares  shown 
in  Fig.  129  are  exactly  the  same  size, 
yet  the  white  square  on  the  black 
ground  appears  larger  than  the  black 
square  on  the  white  ground.  Also 
in  Fig.  130,  the  heavy  black  lines 
appear  to  converge,  though  in  reality 

they  are  parallel.  Illustration  of  irradiation 

,  ,  ,  (McKendnck). 

Clearness  of  vision  depends  on  the 

space  between  the  cones  in  the  point  of  clearest  vision,  the 
macula  hi  tea.  It  has  been  calculated  that  an  object  must 
subtend  an  arc  of  at  least  60  to  70  seconds  in  the  field  of 
vision  to  be  clearly  seen.  Such  an  object  makes  an  image  of 
about  i2ihroth  of  an  inch  in  the  retina  ;  and  this  is  about  the 
distance  between  the  cones  at  the  macula  lutea.  Similarly, 
two  points  to  be  clearly  distinguished  must  be  separated  suf- 
ficiently to  allow  this  amount  of  separation  in  the  retinal 
image. 

Retinal  red :  When  the  retina  of  a  recently-killed  animal 
is  examined  it  is  colorless ;  but  during  life  or  if  extracted 
without  exposure  to  light,  it  is  of  a  purple-red  hue,  and  the 
color  is  found  in  the  rods  of  the  retina.  It  is  derived  from 
the  pigment  of  the  outer  layer  of  the  retina.  It  is  the  "  ret- 
inal red  "  or  "  visual  purple/7  as  it  is  variously  named,  which 
one  sees  in  the  reflex  of  the  retina. 

Exposure  to  light  destroys  it,  and  for  this  reason  it  was  long 
unknown.  It  disappears  after  a  brief  exposure  to  sunlight, 
about  half  a  minute. 

17— Phys. 


258 


THE 


By  throwing  a  beam  of  light  into  the  eye  by  a  mirror,  as 
by  the  ophthalmoscope,  a  red  glow  is  observed  in  the  pupil. 

FIG.  130. 


Nl 

s 
s 

N 
N 
S 

S 

S 

N 
S 
N 

S 

s 

N 
S 
N 

S 

L. 

M 

S  / 

s  / 

V 

1 

\  X 

s  / 
s  / 
s  x 
s  x 

V 

II 

I 

11 

s  x 

V 
V 

k.      JM 

II 

S    w 

1 

% 

II 

s 

s 
s 
s 
s 
s 
s 
s 
s 
s 
s 
s 

KK 
s 

s 

s 

Zollner's  figure  showing  an  illusion  of  direction  (McKendrick). 

This  is  called  the  retinal  reflex.  The  red  glow  is  produced 
by  the  retinal  red. 

Optograms  are  pictures  which  appear  upon  the  retina  after 
exposure  to  light.  They  are  due  to  the  fact  that  an  exposure 
to  light  bleaches  the  retinal  red,  leaving  it  dark  in  the  shaded 
portions. 

An  optogram  may  be  obtained  by  the  following  experi- 
ment: The  eye  is  removed  from  an  animal  in  a  dark  room 
and  kept  in  a  covered  box  until  exposed  to  a  brightly  illumi- 
nated skylight  or  window  for  some  minutes.  The  eye  is  then 
replaced  in  the  dark  room  and  the  retina  examined.  It  will 
he  found  that  the  panes  of  the  window  are  shown  in  light 
color,  while  the  sash  is  in  dark  outline.  This  soon  fades  on 
exposure  to  daylight;  but  if  the  retina  is  dried  in  the  dark, 
the  optogram  is  much  more  durable. 


AFTER-IMAGES.  259 

Pigment  of  choroid  and  retina :  The  student  must  not  con- 
found the  "  visual  purple  "  with  the  pigment  granules  of  the 
choroid  and  retina.  The  latter  are  dark  brown  or  black,  and 
serve  to  keep  the  chamber  of  the  eye  as  a  dark  box.  The 
black  cloth  of  the  photographer  serves  the  same  purpose. 
All  optical  instruments  are  painted  black  on  the  inside  to 
prevent  un desired  reflection  of  light.  So  with  the  eye. 

Color-perception  :  It  is  probable  that  particular  rods  and 
cones  are  capable  of  responding  to  rays  of  light  of  a  certain 
wave-length,  and  to  those  rays  alone.  It  is  well  known  that 
the  rays  of  red  light  are  of  a  certain  length  of  vibration. 
The  same  is  true  of  yellow  and  of  green  rays.  We  can  con- 
ceive that  each  primary  color  has  its  own  set  of  cones  and 
rods  capable  of  responding  to  its  stimulus,  and  that  by  com- 
binations of  these  stimuli  the  complementary  colors  and  varia- 
tions of  shade  may  be  perceived  by  the  resulting  stimuli  act- 
ing upon  the  brain-centres.  Such  teaching  is,  of  course, 
speculative,  but  this  is  one  theory  which  has  acceptance. 

Achromatism :  If  in  obtaining  an  image  of  an  object 
through  a  double  convex  lens  the  lens  be  too  large,  there  will 
be  seen  around  the  image  formed  a  halo  of  prismatic  colors. 
This  is  called  a  chromatic  ring,  and  is  produced  by  an  un- 
equal refraction  of  light-rays  by  the  peripheral  portions  of  the 
lens.  The  unequal  refraction  results  in  a  dispersion  of  the 
light,  so  that  it  is  broken  up  into  the  seven  primary  colors. 
To  remedy  this  defect,  we  put  a  "photographic  shutter"  in 
front  of  the  lens,  thus  limiting  the  entrance  of  light  to  the 
central  portions  of  the  lens,  where  the  index  of  refraction  is 
"  constant "  or  "  true."  In  the  eye  the  iris  acts  as  the  pho- 
tographic shutter,  thus  rendering  the  image  achromatic.  It 
may,  however,  be  said  that  there  may  be  a  visible  band  of 
color  seen  by  some  defective  eyes  where  there  is  considerable 
fault  in  the  focus  of  the  image  on  the  retina. 

After-images :  It  has  already  been  noted  that  vision  lasts 
longer  than  the  stimulus  which  excites  it.  Under  some  con- 
ditions it  may  last  a  perceptibly  long  time  :  it  is  then  known 
as  an  after-image.  If  one  looks  at  an  intense  light,  the  sun, 
the  sense  of  light  remains  for  some  time  in  the  eye.  Similarly, 
if  one  looks  intently  at  a  white  spot  on  a  black  background, 


260  THE  SENSES. 

and  then  turns  to  a  white  surface,  one  has  the  image  of  a 
gray  spot.  The  first  of  these  conditions  cited  is  known  as  a 
positive  after-image,  and  the  latter  as  a  negative.  In  the 
first  case  the  phenomenon  results  as  a  continuation  of  the 
same  sensation,  and  in  the  latter  a  new  perception  results. 

These  images  appear  to  have  the  complementary  color  of 
the  original  object ;  thus,  green  excites  a  reddish  after-image  ; 
orange,  blue  ;  and  so  on.  They  may  be  explained  as  a  result 
of  exhaustion.  The  part  of  the  retina  on  which  the  image 
has  fallen  becomes  tired,  and  when  the  eye  is  turned  upon  a 
white  ground,  the  white  light  coming  to  the  retina  docs  not 
produce  as  much  sensation  in  the  tired  portion.  The  colored 
negative  after-images  may  be  similarly  explained. 

Near-point :  The  "  near-point "  is  the  nearest  point  to  the 
eye  at  which  vision  is  distinct,  the  shortest  focus  of  the  crys- 
talline lens.  It  is  usually  about  five  or  six  inches. 

Defective  eyes  :  Although  hardly  within  the  scope  of  physi- 
ology, it  may  be  perfectly  appropriate  to  discuss  here  some  of 
the  more  common  defects  of  the  eyes  depending  on  abnormal 
conditions  in  the  optical  apparatus. 

Emmetropic  eye  :  It  is  the  normal  eye — that  is,  an  eye 
in  which  parallel  rays  or  rays  from  objects  at  a  distance  are 
focussed  upon  the  retina  without  an  effort  at  accommodation. 
Such  a  distance,  for  practical  purposes,  is  considered  to  be  any 
point  beyond  twenty  feet.  Absolutely  emmetropic  eyes  are 
not  common. 

Myopia  or  "  near  sight "  is  the  term  applied  to  an  eye  in 
which  the  rays  from  a  distance  are  focussed  in  front  of  the 
retina,  and  the  image  is  blurred.  Such  an  eye  is  permanently 
focussed  for  near  objects  (Fig.  132). 

Myopia  is  produced  in  two  ways — by  the  antoro-posterior 
diameter  of  the  eye  being  too  great,  or  by  the  convexity  of 
the  lens  being  exaggerated.  In  either  case  the  focus  of  the 
lens  will  fall  in  front  of  the  retina. 

The  first  condition  is  essentially  a  congenital  defect, 
whereas  too  great  convexity  of  the  lens  may  be  either  con- 
genital or  the  result  of  disease. 

Myopia  is  corrected  by  the  use  of  a  concave  Ions  which 
diverges  the  rays,  and  in  this  way  prevents  their  coming  to  a 


PRESBYOPIA. 


261 


focus  too  soon.     Such  glasses  are  seldom  needed  except  for 
distant  vision. 

Hypermetropia,  or  "far  sight/7  is  the  reverse  of  myopia 
(Fig.  131).     In  hypermetropia  the  antero-posterior  axis  of 


FIG.  131. 


the  eye  is  too  short,  or  else  there  is  an  abnormal  flattening  of 
the  lens,  which  does  not  allow  accommodation  for  near  vision. 
The  result  is  that  the  image  of  an  object  near  by  is  focussed 
behind  the  retina ;  but  objects  at  a  distance  are  clearly  seen. 


FIG.  132. 


Hypermetropic  eye  and  myopic  eye  (far-sighted  and  near-sighted  eye).  1,  hyper- 
metropic  eye.  The  luminous  rays  arriving  from  an  infinite  distance  (parallels) 
produce  an  ocular  cone,  the  summit  of  which  falls  beyond  the  retina  (at  A), 
either  because  the  cone  is  too  long  (lack  of  converging  power  in  the  media  of 
the  eye),  or  because  the  retina  is  too  far  forward  (the  eye  being  too  short) ;  2, 
myopic  eye  ;  the  luminous  rays  from  an  infinite  distance  (parallels)  produce  an 
ocular  cone,  the  summit  of  which  falls  in  front  of  the  retina  (at  B),  either  be- 
cause this  cone  is  too  short  (excess  of  converging  power  in  the  media),  or  be- 
cause the  retina  is  placed  too  far  back  (the  eye  being  too  long).  Bonder's  re- 
searches seem  to  show  that  short-sightedness  is  owing  to  this  latter  cause,  as  is 
well  shown  in  the  figure  (the  ocular  globe  being  greatly  elongated  from  back  to 
front)  (Kuss). 

Hypermetropia  is  corrected  by  the  use  of  convex  lenses, 
which  add  to  the  refractive  power  of  the  eye. 

Presbyopia  is  defective  vision  due  to  the  loss  of  power  in 
advanced  years.  The  elasticity  of  the  lens  becomes  less,  and 
the  convexity  cannot  be  increased  for  near  vision.  The 


262  THE  SENSES. 

ciliary  muscle  may  also  be  weaker  and  aid  in  the  production 
of  the  error.  A  weak  convex  glass  commonly  corrects  the 
lack  of  refraction-power. 

Thus  we  see  that  presbyopia  is  identical  with  hypermetropia 
due  to  flattening  of  the  lens. 

Astigmatism  is  a  defect  in  the  vision  due  to  the  irregularity 
in  the  globe  of  the  eye,  whereby  the  diameter  in  one  plane  is 
greater  than  in  another.  Thus,  the  retina  may  be  an  uneven 
surface,  and  the  image  focus  accurately  in  one  part  and  falsely 
in  another.  In  this  condition  vertical  and  horizontal  lines  are 
not  seen  with  equal  distinctness. 

Astigmatism  is  corrected  by  the  use  of  cylindrical  or  pris- 
matic glasses,  which  have  to  be  accurately  adapted  to  the 
needs  of  each  case.  This  error,  if  serious,  is  usually  com- 
bined with  other  defects  of  vision,  frequently  myopia. 

Diplopia  is  the  condition  which  results  from  a  want  of  har- 
mony in  the  eyes,  so  that  the  image  of  each  eye  is  perceived 
separately  ;  that  is,  one  sees  double. 

Diplopia  is  commonly  caused  by  paralysis  or  spasm  in  one 
of  the  lateral  straight  muscles,  which  does  not  allow  the  eye 
to  be  turned  in  harmony  with  the  other.  If  the  eyes  are  turned 
so  that  the  axes  of  vision  are  separated,  the  condition  is 
known  as  external  strabismus  or  squint ;  if  the  axes  are  crossed, 
it  is  called  internal  strabismus  or  cross-eye. 

Color-blindness  is  an  inability  to  perceive  some  colors.  The 
colors  which  are  usually  mistaken  are  green  and  red.  Fre- 
quently it  is  found  that  a  distinction  cannot  be  made  between 
these  colors.  This  is  sometimes  known  as  Daltonism. 

Theories  of  normal  color-perception :  Ordinary  white  light 
if  decomposed  is  resolved  into  the  seven  primary  colors — 
violet,  indigo,  blue,  green,  yellow,  orange,  and  red.  Each 
of  these  primary  colors  has  a  different  wave-length.  Other 
colors  than  the  seven  primary  colors  are  the  result  of  the 
mixture  of  two  or  more  of  the  primary  colors  in  various 
proportions.  We  are  ignorant  of  the  manner  in  which  the 
rods  and  cones  are  made  to  vibrate  by  ordinary  images, 
and  we  are  equally  ignorant  as  to  the  nature  of  the  process 
that  allows  the  diiVcrcnt  color-effects  to  be  conveyed  to  the 
optic  nerve. 


THEORIES  OF  NORMAL   COLOR-PERCEPTION.       263 

As  it  is  impossible  to  go  fully  into  the  matter  in  this  book, 
it  is  hoped  that  the  following  will  suffice : 

The  different  color  theories  assume  that  there  are  different 
substances  in  the  retina  capable  of  responding  to  different 
wave-lengths  of  light  (comparable  to  a  photo-chemical  pro- 
cess). 

Red,  green,  and  violet  (Fig.    133)  are  the   fundamental 

FIG.  133. 


Diagram  of  three  primary  color-sensations.  1  is  the  so-called  " red,"  2  "green,"  and 
3  "violet"  primary  color  sensation;  R,  0,  Y,  etc.,  represents  the  red,  orange, 
yellow,  etc.,  color  of  the  spectrum,  and  the  diagram  shows,  by  the  height  of  the 
curve  in  each  case,  to  what  extent  the  several  primary  color-sensations  are  re- 
spectively excited  by  vibrations  of  different  wave-lengths  (Foster). 

colors,  and  all  others  may  be  made  from  combinations  of  these 
three. 

Working  on  this  basis,  Young  and  Helmholtz  assumed 
three  chemical  substances  in  the  retina  capable  of  replying 
to  the  three  fundamental  colors. 

Hering  assumed  three  substances  responding  respectively 
to  white  or  "  black "  (absence  of  light),  red  or  green,  and 
yellow  or  blue  light.  In  this  theory  the  white,  red,  and  yel- 
low rays  are  katabolic  in  their  effect  on  their  individual  re- 
cipient substances;  the  "black/7  green,  and  blue  being  ana- 
bolic— e.  g.j  the  substance  responding  to  white  is  "broken 
down "  by  white  light,  but  is  regenerated  ("built  up")  by 
"black  light" — i.  e.,  absence  of  light.  Mrs.  Franklin  assumes 
in  her  theory  that  in  early  life  the  eye  possesses  no  color-per- 
ception, but  merely  perception  of  luminosity — i.  e.,  white  or 


264  THE  SENSES. 

black.  The  substance  responding  to  luminosity  she  calls 
"  gray-perceiving."  As  the  development  progresses,  some  of 
the  "  gray "  is  differentiated  into  a  blue-  and  a  yellow-per- 
ceiving substance.  The  yellow-perceiving  substance  is  still 
further  differentiated  in  the  course  of  development  into  a  red- 
and  a  green-perceiving  substance  ;  thus  : 

Gray. 

I 


Blue.  Yellow. 

I 


Green.  Red. 

Many  objections  have  been  raised  against  each  of  these 
three  color-theories,  and  it  is  true  that  each  leaves  some  points 
unexplained ;  but  Mrs.  Franklin's  is,  so  far,  the  best,  and 
more  readily  explains  the  peculiarities  of  color-blindness. 

Causes  of  color-blindness  :  The  followers  of  Helmholtz  and 
Hering  say  that  color-blindness  is  due  to  an  absence  of  one 
or  more  of  the  fundamental  color-perceiving  substances. 

Mrs.  Franklin's  theory  assumes  a  lack  of  full  development 
or  complete  absence  of  development  of  the  "  gray  "-perceiv- 
ing substance. 

Thus,  in  a  case  of  absolute  color-blindness  the  "  gray " 
substance  has  undergone  no  development,  and  the  individual 
sees  everything  as  without  color,  but  in  different  shadings  of 
light  or  darkness.  To  such  a  person  a  highly  colored  paint- 
ing would  look  like  a  black-and-white  etching. 

Again,  working  on  the  development  theory,  we  may  assume 
that  the  gray  differentiated  into  "blue"-  and  "  yellow  "-per- 
ceiving substances  and  there  stopped.  Clinically  we  find  in- 
dividuals capable  of  distinguishing  blues  and  yellows,  but 
reds  and  greens  are  unknown  to  them. 

Color-blindness  in  different  sexes:  Males  are  far  more  liable 
to  be  color-blind  than  female  (16  to  1).  Only  about  one 
woman  in  four  hundred  is  color-blind.  The  reason  for  the 
preponderance  of  color-blind  men  may  be  accounted  for  on 
the  theory  that  although  the  differentiation  of  the  "gray"- 
perceiving  substance  into  red,  green,  and  blue  is  a  natural 


TEST  FOR   COLOR-BLINDNESS.  265 

process,  nevertheless  it  can  be  perfected  by  practice  and  color- 
education.  Such  an  education  is  given  early  in  life  to  little 
girls  in  matching  colors  for  doll's  clothing,  etc.,  whereas,  it  is 
neglected  in  boys. 

Importance  of  the  defect :  In  marine  and  land  locomotion, 
red  and  green  signals  are  used  to  indicate  opposite  conditions, 
and  the  failure  to  distinguish  them  has  frequently  been  the 
cause  of  serious  accidents. 

Test  for  color-blindness :  By  laying  a  number  of  skeins  of 
yarn  of  various  colors  in  a  heap,  and  requiring  the  person  to 
be  tested  to  select  all  resembling  a  certain  skein  from  the 
heap. 


EMBRYOLOGY. 


Embryology  deals  with  the  reproduction  and  development  of 
individuals,  whether  of  animal  or  plant  life.  AVe  shall  first 
study  how  the  parent  gives  origin  to  the  offspring,  and  later 
on  the  development  of  that  offspring  until  it  becomes  a  fully 
developed  member  of  its  species. 

REPRODUCTION. 

By  species  we  mean  a  class  of  organized  beings  in  which 
the  individuals  composing  it  die  off,  but  which  nevertheless 
repeats  itself  and  maintains  its  complement  by  the  continued 
accession  of  similar  forms. 

Heredity  is  the  inherent  property  of  the  individual  by 
virtue  of  which  the  individual  is  of  the  same  species  as  the 
parent,  and  furthermore  has  certain  individual  characteristic's 
of  the  parent.  We  are  human  beings  because  our  parents 
were  human  beings,  and  we  inherit  the  form  and  character- 
istics of  the  species.  Still  further,  we  may  have  certain 
tricks  of  speech,  a  peculiar  gait  or  method  of  thinking,  in- 
herited from  our  individual  parents. 

Reproduction  is  the  process  by  which  a  species  is  perpetu- 
ated, notwithstanding  the  limited  existence  of  the  individual 
members. 

The  law  governing  reproduction  is  that  the  young  are  of 
the  same  kind  as  their  parents.  By  this  law,  which  i-  s<> 
commonly  observed  as  to  seem  a  truism,  is  maintained  the 
anatomical  identity  of  individuals  of  a  species,  as  well  as  the 
physiological  fact  of  an  unbroken  continuance  of  the  species 
by  reproduction. 

Methods  of  reproduction :  Reproduction  takes  place  by  one 

266 


THEORY   OF  REPRODUCTION.  267 

of  two  entirely  distinct  methods — asexual  reproduction  and 
sexual  reproduction. 

Asexual  reproduction  is  the  usual  method  among  plants 
and  animals  whose  organism  consists  of  but  one  cell.  It  is 
also  the  method  in  some  of  the  lower  multicellular  animals 
and  many  higher  forms  of  plants. 

When  considering  the  amoeba  it  was  stated  that  it  sub- 
divided, with  the  result  that  from  the  single  cell  we  had 
two  distinct  units,  each  being  members  of  the  same  species. 
No  sexual  relations  have  taken  place,  and  the  offspring  is  the 
child  of  but  one  parent. 

Sexual  reproduction :  Sexual  reproduction  consists  of  the 
union  of  elements  produced  separately  by  the  female  and  the 
male.  In  some  of  the  lower  organisms  there  is  no  direct 
output  from  the  male  and  female,  but  the  two  parents  fuse 
together,  and  the  resultant  mass  develops  into  the  offspring ; 
such  a  method  is  called  "  conjugation." 

As  we  rise  in  the  animal  scale  we  find  that  the  female 
produces  the  ovum,  or  egg,  which  is  capable  of  being  devel- 
oped into  a  living  offspring  only  when  it  is  fecundated  or  im- 
pregnated by  the  seminal  or  spermatic  element  from  the  male. 

In  some  animals  (worms)  both  the  male  and  female  ele- 
ments exist  in  the  same  individual ;  but  still  the  offspring  is 
the  result  of  "  sexual  reproduction,"  although  there  is  but 
one  parent. 

Theory  of  reproduction:  Just  why  a  cell  should  subdivide 
into  two  secondary  cells,  or  why  there  should  be  the  necessity 
for  sexual  reproduction,  is  a  difficult  problem  to  answer. 

Asexual  generation  may  be  explained  according  to  certain 
principles  laid  down  by  Herbert  Spencer.  Spencer  pointed 
out  conclusively  that  the  mass  of  a  cell  grows  as  the  cube, 
whereas  the  surface  grows  only  as  the  square ;  from  this  it 
follows  that  the  mass  to  be  nourished  soon  outgrows  the  ab- 
sorbing or  nourishing  surface,  hence  fission  results  to  insure 
a  relative  increase  of  surface  to  the  mass.  Such  division  of 
cells  goes  on  for  a  variable  number  of  times,  until  finally  the 
cell-protoplasm  becomes  enfeebled  and  worn  out.  In  certain 
infusoria  the  number  of  divisions  may  be  from  150  to  450; 
after  that  conjugation  is  necessary  for  a  continuance  of  the 


268  REPRODUCTION. 

method.  From  such  observations  one  may  reason  that  sexual 
reproduction  insures  a  fresh  conjugation  of  protoplasm  for 
each  individual,  thus  keeping  the  standard  up  to  the  maxi- 
mum. 

Also  sexual  reproduction  tends  to  preserve  the  type  of  the 
species  ;  for  if  the  individual  were  the  offspring  of  but  one 
parent,  certain  characteristics  of  that  parent  would  be  exag- 
gerated in  the  course  of  several  generations;  but  as  the 
individual  springs  from  two  parents,  it  becomes  the  menu 
between  those  parents,  with  the  result  that  the  individual 
tends  to  become  the  composite  of  the  entire  species. 

Fecundation  :  The  junction  of  the  male  and  female  delimit* 
in  sexual  generation  is  called  fecundation.  At  the  time  when 
the  male  and  female  discharge  their  respective  elements  it  is 
not  necessary  that  the  parents  should  be  in  juxtaposition.  In 
deep-sea  fishes  the  female  discharges  her  spawn  ;  the  male, 
which  is  destined  to  fecundate  these  ova,  may  be  miles  away 
and  discharge  his  spermatozoa  into  the  ocean  ;  the  male  and 
female  elements  may  float  about  until  finally  they  meet,  with 
the  result  that  the  ova  become  fecundated. 

In  fishes  like  trout,  salmon,  etc.,  the  female  lays  her  eggs 
on  the  spawning-bed,  and  later  on  the  male  deposits  his  ele- 
ments directly  on  the  spawn. 

Still  further  along  in  the  scale  we  find  juxtaposition  essen- 
tial, the  male  grasping  the  female  and  both  discharging  their 
elements  at  the  same  time,  and  the  ova  are  fecundated  as  soon 
as  they  leave  the  female. 

Of  course,  in  "  viviparce  "  not  only  is  juxtaposition  essential, 
but  there  is  an  actual  discharge  of  the  male  elements  into  the 
cavity  of  the  female  generative  organs  (such  an  act  is  called 
"  copulation  "). 

Human  Female  Organs  of  Generation. 

The  female  organs  consist  of  two  or  (trie*,  in  which  the 
ova  are  formed,  and  their  oviducts  or  F<ill«i>i<tn  ////«•*,  which 
carry  the  ova  to  the  uterus,  in  which  they  may  develop  if 
fecundated  by  the  male  ;  and  the  ntf/hia  for  the  reception  of 
the  male  organ  in  copulation  and  for  the  subsequent  discharge 
of  the  foetus. 


GRAAFIAN  FOLLICLES. 


269 


The  ovaries  are  two  organs  lying  one  on  each  side  of  the 
uterus,  attached  to  the  broad  ligament.  In  size  they  are 
about  1J  inches  long,  1  inch  wide,  and  l  inch  in  thickness. 
Besides  their  attachment  to  the  broad  ligament,  they  are 
stayed  in  their  position  by  folds  or  ligaments  running  to  the 

FIG.  134. 


Generative  organs  of  the  human  female,  a,  a,  ovaries ;  &,  b,  Fallopian  tubes  ;  c,  body 
of  the  uterus ;  d,  cervix  ;  e,  vagina  (upper  part). 

fund  us  of  the  uterus  and  to  the  fimbriated  extremity  of  the 
Fallopian  tube. 

If  an  ovary  be  minutely  examined,  it  is  seen  to  be  a  duct- 
less gland  in  which  the  composing  elements  are  :  (1)  A  stroma 
of  connective  tissue  and  unstriped  muscle-cells,  and  with 
them  a  great  number  of  peculiar  spindle-shaped  branching 
cells  ;  and  (2)  the  glandular  portion,  characterized  by  the 
Graafian  follicles. 

The  Graafian  follicles  are  best  observed  during  the  child- 
bearing  age.  They  lie  in  the  periphery,  and  present  various 
appearances  as  they  are  more  or  less  matured.  Some  are 
large  enough  to  be  seen  by  the  unaided  eye,  while  others  are 
very  minute.  In  the  matured  follicle  the  interstitial  tissue 
will  be  found  to  have  collected  in  a  wall,  quite  well  defined, 
which  is  lined  by  an  epithelial  layer ;  and  upon  one  of  this 


270 


REPRODUCTION. 


FIG.  135. 


Human  ovum,  ruptured  by 
pressure,  showing  the  vitel- 
lus  partially  expelled,  the 
germinative  vesicle,  with  its 
germi native  spot,  at  o,  and 
the  smooth  fracture  of  the 
vitelline  membrane. 


layer  epithelium  is  heaped  up  into  a  mass,  the  germ-hill 
(cumulus  or  discus  proligerus),  which  contains  the  ovum.  The 
remainder  of  the  follicle  is  filled  with  a  colorless  fluid. 

As  the  Graafian  follicles  mature  they  approach,  and  often 
project  above,  the  surface  of  the  ovary.  The  fluid  contents 
of  the  follicle  increase  and  the  wall 
becomes  thinner  over  it,  until  finally 
it  bursts,  and  the  ovum  with  some 
of  its  surrounding  epithelium  escapes. 
The  ovary  is  covered  on  one  sur- 
face with  a  thin  layer  of  epithelium 
(the  germinal  epithelium),  and  not  by 
the  peritoneum.  This  is  of  great 
importance  in  the  life  of  the  ovum, 
for  it  renders  it  possible  for  it  to  en- 
ter the  orifice  of  the  Fallopian  tube 
without  interfering  with  the  peri- 
toneum and  without  having  to  pass  so 
dense  a  structure. 

From  puberty  to  the  menopause 

the  formation  of  new  Graafian  follicles  is  continuous,  and  a 
very  great  number  are  produced  ;  but  many  do  not  develop 
ova,  and  so  waste  away  without  going  through  the  changes 
described. 

The  ovum  is  a  very  highly  developed  cell,  which  is  derived 
from  the  germinal  epithelium  covering  the  ovary.  In  the 
development  of  the  ovary  this  epithelium  dips  into  the  sur- 
face of  the  organ,  and  a  certain  portion  is  finally  walled  oil' 
by  growth  of  the  surface-cells.  Thus  a  ball  of  epithelial  cells 
is  introduced  into  the  body  of  the  organ,  and  one  cell  devel- 
ops the  ovum,  the  rest  going  on  to  make  up  the  (Jraafiau  fol- 
licle and  the  germ-hill  (see  5,  6,  7,  8,  9,  Fig.  136). 

If  the  ovum  in  its  perfected  state,  as  it  leaves  the  Graafian 
follicle,  be  examined,  it  will  be  found  to  be  a  minute  globular 
cell  containing  a  nucleus  and  nucleolus  as  well  as  a  cell- 
membrane. 

In  diameter  the  ovum  is  a  little  less  than  yj-^th  inch.  The 
component  parts  of  the  ovum  have  received  special  names  and 
are  worthy  of  separate  description. 


THE  OVUM. 


271 


The  cell-wall  is  called  the  "  zona  pellucida"  or  "  radiata"  or 


FIG.  136. 


Section  of  the  ovary  (after  Schron).  1,  outer  covering;  1',  attached  b9rder :  2,  cen- 
tral stroma  ;  3,  peripheral  stroma ;  4,  bloodvessels ;  5,  Graafian  follicles  in  their 
earliest  stage ;  6,  7, 8,  more  advanced  follicles  ;  9,  an  almost  mature  follicle;  9', 
follicle  from  which  the  ovum  has  escaped;  10,  corpus  luteum. 


(IV 


Semi-diagrammatic  representation  of  a  mammalian  ovum  .highly  magnified,    zp, 
zona  pellucida ;  vi,  vitellus  ;  gv,  germinal  vesicle  ;  gs,  germinal  spot. 

"  vitelline  membrane,"  and  is  a  thick  hyaline  membrane  enclos- 
ing the  cell-body. 


272  REPRODUCTION. 

The  cell-body  is  a  mass  of  granular  protoplasm,  called  the 
"  vitellus." 

The  cell-nucleus,  or  "germinal  vesicle"  is  a  somewhat  large 
transparent  and  well-defined  body  set  somewhat  eccentrically 
in  the  vitellus  or  egg-yolk. 

The  nucleolus  of  the  cell  is  called  the  "germinal  spot." 
The  latter  is  a  small,  dark,  almost  opaque  spot,  situated  in  the 
nearly  transparent  fluid  nucleus  (Fig.  135). 

Fallopian  tubes  :  The  tubes  are  about  3^  inches  in  length, 
and  extend  from  the  fundus  of  the  uterus  laterally  on  each 
side.  The  calibre  of  the  tubes  gradually  narrows  from  with 
out  inward,  until  at  the  uterus  the  opening  is  very  minute. 
The  external  covering  is  peritoneum,  but  the  lining  is  mucous 
membrane  having  ciliated  epithelium.  The  outer  end  of  the 
Fallopian  tube  is  free  and  fringed — the  fimbriated  extremity. 

The  function  of  the  fimbriated  extremity  is  to  grasp  the 
ovary,  and  thus  act  as  a  funnel  into  which  the  ovum  is  dis- 
charged by  the  rupture  of  the  Graafian  follicle.  It  frequently 
happens  that  ova  are  expelled  from  the  ovary  and  miss  the 
mouth  of  the  fimbriated  end  of  the  Fallopian  tube,  either  be- 
cause the  fimbrium  failed  to  grasp  the  ovary  at  the  proper 
point  or  else  had  failed  altogether  to  make  any  attempt  to 
grasp  the  ovary.  Under  such  circumstances  the  ovum  lodges 
in  the  peritoneal  cavity  and  usually  dies,  but  occasionally  be- 
comes impregnated. 

Between  the  peritoneal  covering  of  the  Fallopian  tube  and 
its  mucous  membrane  lining  is  a  coat  of  circular  and  longi- 
tudinal muscle-fibres.  These  muscle-fibres  serve  to  force  the 
ovum  received  by  its  fimbriated  end  along  the  tube,  and  so 
into  the  uterus.  This  action  is  also  aided  by  the  ciliated 
epithelium. 

The  uterus  is  a  somewhat  pear-shaped  organ,  and  is  about 
3  inches  in  length,  its  wider  part  being  about  2  inches  wide 
and  the  cervix  1  inch.  It  is  described  as  consisting  of  a 
fundus,  body,  and  cervix.  This  body  unites  the  fundus  with 
the  cervix,  which  extends  into  the  vagina. 

It  is  covered  over  nearly  all  of  its  external  surface  with 
peritoneum.  Its  bulk  is  made  a p of  un striped  muscle,  which 
occurs  in  longitudinal  and  circular  bundles  and  layers.  This 


PUBERTY.  273 

muscular  tissue  increases  enormously  during  pregnancy,  and 
by  its  strength  helps  to  extrude  the  foetus.  The  lining  is  of 
mucous  membrane,  which  is  formed  in  its  superficial  layer  of 
ciliated  columnar  epithelium.  In  the  mucous  membrane  of 
the  cervix  are  a  number  of  follicles  which  secrete  a  viscid, 
tenacious  mucus,  by  which  the  os  uteri  is  frequently  found 
to  be  plugged. 

The  vagina  is  a  musculo-membranous  canal  about  5  inches 
long,  extending  from  the  uterus  to  the  external  genitals.  It 
is  lined  with  mucous  membrane,  which  in  the  ordinary  con- 
tracted state  is  thrown  into  folds,  its  anterior  and  posterior 
walls  being  in  contact.  There  is  considerable  erectile  tissue 
in  the  mucous  membrane.  At  the  orifice  of  the  vagina  ex- 
ternally is  a  sphincter  which  only  partially  contracts  it,  and 
besides  this  there  are  longitudinal  and  transverse  unstriped 
muscle-fibres  in  the  submucous  tissue.  The  outlet  of  the 
vagina  is  sometimes  also  partially  closed  in  the  virgin  by  the 
hymen,  a  fold  of  mucous  membrane. 

The  external  organs  of  generation  are  not  immediately  con- 
nected with  the  function  of  reproduction,  and  may  be  enu- 
merated as  the  labia  majora,  labia  minora,  and  clitoris. 

Functional  activity  of  female  generative  organs  :  Under  this 
heading  we  have  two  manifestations  to  study — viz.,  ovulation 
and  menstruation.  Both  of  these  events  are  closely  associated 
with  the  childbearing  period  of  a  woman's  life,  and  are  also 
closely  associated  together.  Much  dispute  has  arisen  over 
the  association  of  menstruation  and  ovulation,  and  without 
attempting  to  weigh  the  comparative  merits  of  the  different 
theories  we  shall  accept  and  describe  only  those  most  gen- 
erally accepted. 

Menstruation  is  a  phenomenon  inherent  in  all  women  be- 
tween puberty  and  the  menopause.  It  consists  of  a  flow  of 
blood  from  the  uterus,  together  with  an  exfoliation  of  part  or 
of  the  whole  of  the  mucous  membrane  of  the  uterus.  At  the 
menstrual  period  there  are,  in  addition,  certain  physical  and 
psychical  manifestations  involving  to  a  more  or  less  degree 
the  entire  individual. 

By  puberty  is  meant  that  age  at  which  a  woman  begins  her 
functional  (childbearing)  existence.  In  temperate  climates 

IS— Phys. 


274  REPRODUCTION. 

we  may  say  the  average  age  is  fourteen  years.  In  southern 
countries  it  is  somewhat  earlier,  and  in  the  arctic  regions  a 
year  or  two  later.  However,  no  fixed  rule  can  be  given,  as 
i he  time  of  arrival  at  puberty  varies  with  every  individual, 
depending  on  race,  temperament,  hygiene,  and  general  sur- 
roundings. 

At  puberty  is  the  time  when  the  girl  changes  into  the 
woman.  The  event  is  not  accomplished  at  once,  but  extends 
over  considerable  time.  The  girl  undergoes  a  gradual  change 
in  figure,  the  hips  broaden,  the  breasts  develop,  pubic  hair 
grows  abundantly,  etc.  She  now  begins  to  realize  the  differ- 
ence in  sex  between  herself  and  her  boy  companions.  She 
becomes  more  bashful  and  retiring.  Also  for  the  first  time  a 
menstrual  flow  is  noticed.  At  first  the  menstrual  periods  are 
scanty  and  irregular,  but  after  a  few  months  they  settle  down 
to  the  characteristic  rate  and  duration.  The  girl  is  now  a 
woman. 

By  menopause,  or  climacteric,  is  meant  the  physiological 
cessation  of  the  menstrual  flow.  The  woman's  functional 
activity  is  over.  The  ovaries  become  smaller ;  no  more 
Graafian  follicles  are  developed  ;  the  Fallopian  tubes  atrophy  ; 
the  pubic  hair  becomes  thin  and  straight.  The  age  of  meno- 
pause varies  as  does  the  age  of  puberty ;  in  general  we  may 
say  the  earlier  the  puberty  the  earlier  the  menopause,  and 
vice  versa.  In  temperate  climates  the  average  period  for 
the  arrival  of  the  menopause  is  at  the  age  of  forty-five  years. 
Thus  we  see  a  woman's  functional  activity  lasts  thirty  years. 

Frequency  of  menstruation  :  When  once  established  men- 
struation occurs  on  the  average  every  twenty-eight  days  al- 
though it  is  not  without  the  bounds  of  normal  health  for 
some  women  to  have  a  menstrual  flow  every  twenty-one  days, 
and  others  do  not  menstruate  oftener  than  once  in  six  weeks. 
Menstruation  is  in  abeyance  during  y>m//m>/r//  and  lactation. 

Duration  of  menstruation:  The  menstrual  flow  lasts  on  an 
average  five  days,  the  amount  of  blood  lost  gradually  in- 
creasing until  the  third  day,  and  then  gradually  diminishing. 

Nature  of  menstruation:  At  the  beginning  of  menstruation 
there  is  a  general  congestion  of  the  generative  organs,  in- 
cluding the  breasts.  A  few  days  before  menstruation  there 


LIFE-HISTORY  OF  THE   UNIMPREGNATED   OVUM      275 

has  developed  a  hypertrophy  of  the  mucous  membrane  (su- 
perficial layers)  of  the  uterus.  At  the  beginning  of  the 
menstrual  period  this  hypertrophied  mucous  membrane  is 
gradually  shed,  leaving  its  underlying  vessels  exposed,  and 
they  bleed.  At  the  end  of  menstruation  a  new  mucous  mem- 
brane is  developed.  The  shed  mucous  membrane  is  called 
the  "decidua  menstrualis."  During  menstruation,  especially 
t  the  beginning  of  the  period,  the  woman  is  apt  to  be 
peevish,  irritable,  complains  of  headache,  loss  of  appetite, 
and  a  sense  of  pelvic  oppression  that  may  even  amount  to 
severe  pain. 

Character  of  menstrual  discharge :  It  is  a  thin,  bloody  fluid 
of  a  dark  color  and  having  a  peculiar  odor.  It  consists  of 
blood,  epithelium,  and  mucus  from  the  uterus  and  vagina,  to- 
gether with  the  decidua  menstrualis.  The  blood  does  not  clot. 

Ovulation :  The  commonly  accepted  theory  is  that  about  or 
shortly  before  the  age  of  puberty  the  Graafian  follicles  begin 
to  discharge  their  ova,  and  that  this  process  continues  until 
the  menopause.  Doubtless  many  Graafian  follicles  only  par- 
tially develop  and  atrophy  without  discharging  mature  ova. 
The  frequency  with  which  well-developed  ova  are  discharged 
is  the  subject  of  much  dispute.  The  most  conservative  view 
is  that  there  is  one  mature  ovum  discharged  for  each  men- 
strual epoch.  On  the  other  hand,  other  embryologists  claim 
that  there  is  an  almost  daily  discharge  of  ova,  but  only  a  few 
enter  the  Fallopian  tubes,  while  the  rest  are  lost  in  the  peri- 
toneal cavity.  Whichever  view  the  student  cares  to  follow  is 
immaterial,  but  nevertheless  we  must  agree  that  only  about 
as  many  mature  ova  reach  the  uterine  cavity  as  there  are 
menstrual  epochs. 

Life-history  of  the  unimpregnated  ovum :  On  leaving  the  ovary 
and  entering  the  Fallopian  tube  the  ovum  is  surrounded  by 
a  few  cells  derived  from  the  discus  proligerus  of  the  Graafian 
follicle.  These  cells  may  serve  as  a  source  of  nourishment, 
but  soon  disappear.  There  are  now  certain  changes  to  be 
observed  in  the  ovum  itself;  first,  the  vitelline  substance 
seems  to  contract  slightly,  so  as  to  leave  a  narrow  rim  or 
space  between  the  vitellus  and  zona  pellucida — the  peri  vitel- 
line space. 


276  REPRODUCTION. 

At  this  time  the  nucleus  or  germinal  vesicle  undergoes  a 
karyokinetic  division  into  two  parts,  one  part  then  being  ex- 
pelled from  the  ovum  proper  into  the  peri vitel line  space  as  a 
"polar  body"  the  remaining  portion  of  the  original  nucleus, 
again  subdividing  into  two  parts  by  karyokinesis,  with  the 
protrusion  of  one  part  as  a  second  "  polar  body."  What  is 
now  left  of  the  original  nucleus  is  the  "female  pronudeus  "  ; 
the  polar  bodies  are  apparently  useless.  Up  to  this  point  all 
ova  develop  alike,  and  now  are  fit  for  impregnation.  If  im- 
pregnation does  not  take  place,  the  ovum  dies  and  is  caM  nil'. 
If  impregnation  does  occur,  there  is  further  development  of 
the  ovum,  as  we  shall  see  in  a  later  paragraph. 

Corpus  luteum :  After  the  escape  of  an  ovum  there  is  an 
effusion  of  blood  into  the  cavity  of  the  Graafian  follicle. 
The  clot  which  follows  is  disposed  of  by  the  same  retrogressive 
processes  which  extravasated  blood  may  undergo  in  any  part 
of  the  body.  The  serum  is  absorbed,  the  cells  disintegrate. 
and  the  coloring-matter  is  in  part  taken  up  by  the  tissues  and 
in  part  crystallizes  or  takes  up  other  constituents,  and  pre- 
sents variations  of  coloring.  Hand  in  hand  with  these 
changes  in  the  blood  go  important  changes  in  the  surround- 
ing tissues.  The  epithelial  cells  which  are  left  behind  pro- 
liferate and  form  a  sort  of  yellowish,  very  vascular  tissue, 
which  presently  undergoes  fatty  degeneration.  This  yellow 
mass  surrounding  and  enclosing  the  remains  of  the  extrava- 
sated blood  constitutes  the  corpus  £ufeum,and  as  it  disappears 
its  place  is  occupied  by  a  dense,  firm  connective-tissue  cica- 
trix,  which  may  be  pigmented. 

The  changes  described  above  are  those  that  take  place  if 
the  ovum  fails  to  become  impregnated.  If,  on  the  other  hand, 
fecundation  ocvurs,  the  corpus  luteum  undergoes  certain 
characteristic  changes,  widely  differing  from  the  degenera- 
tion of  the  corpus  luteum  of  non-pregnancy.  If  the  ovum  he 
impregnated,  the  corpus  luteum  then  does  not  degenerate  and 
disappear  rapidly  as  after  menstruation,  but  continues  fully 
as  large  as  at  the  beginning  for  several  months,  and  at  the 
end  of  pregnancy  still  remains  as  a  clearly  marked  body. 
This  is  shown  in  the  following  table  from  Dalton : 


MALE  GENERATIVE  ORGANS. 


277 


At  the  end  of 
three  weeks. 
One  month. 


Two  months. 
Four  months. 

Six  months. 
Nine  months. 


Corpus  Luteum  of  Menstrua- 
tion. 

f  inch  in  diameter ;  central 

pale. 
Smaller ;     convoluted     wall 

bright  yellow  ;  clot  still 

reddish. 
Reduced  to  the  condition  of 

an  insignificant  cicatrix. 

Absent  or  unnoticeable. 


, 

\ 


Corpus  Luteum  of  Pregnancy 
(Dal  ton). 

•lot  reddish  ;  convoluted  wall 

Larger ;  convoluted  wall 
bright  yellow ;  clot  still 
reddish. 

|  inch  in  diameter ;  convo- 
luted wall  bright  yellow ; 
clot  perfectly  decolorized. 

Size  about  as  at  two  months; 
clot  pale  and  fibrinous; 
convoluted  wall  dull  yel- 
low. 

Absent.  Still  as  large  as  at  the  end 

of  the  second  month.  Clot 
fibrinous.  Convoluted  wall 
paler. 

Absent.  £  inch  in  diameter ;  central 

clot  converted  into  a  radi- 
ating cicatrix ;  external 
wall  tolerably  thick  and 
convoluted,  but  without 
any  bright  yellow  color. 

Connection  between  ovulation  and  menstruation  :  Whether 
ovulation  depends  upon  menstruation  or  menstruation  upon 
ovulation,  or  whether  either  has  any  connection  with  the 
other,  is  a  matter  of  lengthy  controversy. 

However,  the  general  view  is  that  both  ovulation  and 
menstruation  are  the  result  of  a  common  cause  (cause  un- 
known), but  either  may  exceptionally  occur  without  the 
other. 

It  is  generally  accepted  that  ovulation,  or  discharge  of 
•yum  from  a  Graafian  follicle,  takes  place  a  few  days  before 

e  onset  of  the  menstrual  period. 


Human  male  generative  organs. 


The  generative  organs  of  the  male  consist  of  the  two  tes- 
icks,  which  produce  the  seminal  fluid ;  and  the  vas  deferens, 
»r  duct  leading  from  each  to  join  with  the  duct  of  the  corre- 
ponding  seminal  vesicle,  in  which  the  secretion  is  stored  (?) 

until   it  is  discharged   through  the  penis  and  the  prostate 

gland. 


278 


REPRODUCTION. 


FIG.  138. 


Testicles :  Each  testicle  is  made  up  of  a  dense  connective- 
tissue  framework  and  a  secreting  portion.  The  connective- 
tissue  stroma,  tunica  albuginea,  surrounds  the  outside  of  the 
organ,  and  sends  incomplete  partitions  into  the  central  por- 
tion of  the  organ,  dividing  it  into  a  number  of  communicating 
cavities.  In  these  cavities  are  winding  tubules  which  con- 
stitute the  secreting  portion  of  the  organ.  These  tubules  in- 
osculate in  a  sort  of  mesh  (rete  testis),  and  finally  all  unite  in 
the  epididymis.  The  secreting  tubules  are  called  the  semi- 
niferous tub  lit  ex. 

Each  tubule  has,  in  the  active  organ,  a  limiting  membrane, 
upon  which  are  a  number  of  layers  of  flattened  cells.  In- 
ternal to  these  are  seminal  cells  in  two  or  more  layers.  The 
seminal  cells  contain  nuclei  which  are  capable  of  division,  so 
that  each  nucleus  may  develop  several  new  nuclei.  The 
nuclei  are  the  spermatoblasts,  or  cells  from  which  the  sper- 
matozoa originate.  The  cells  before  the  di- 
vision of  the  nuclei  resemble  the  ordinary 
cuboid  epithelium,  and  it  is  in  the  superficial 
layers  (i.  e.,  toward  the  lumen  of  the  tubuli) 
that  this  function  of  the  cells  takes  place. 

The  seminiferous  tubules  all  converge  to- 
ward the  epididymis,  a  tortuous  tubule  which 
is  lined  with  mucous  membrane,  and  lies 
beside  the  testis  in  a  long,  convoluted  mass 
which  may  be  unravelled,  and  is  found  to  be 
about  20  feet  long.  This  empties  contents, 
or  rather  continues  on,  into  the  va#  dejer- 
ens,  which  conveys  the  semen  to  the  junction 
with  the  seminal  vesicle.  During  this  passage 
the  mucous  membrane  adds  a  viscid  mucous 
secretion  in  which  the  spermatozoa  are  liber- 
ated and,  so  to  speak,  diluted. 

Spermatozoa :    In    the   seminiferous  tubules 
the  developing  spermatozoa  may  be  seen  with 
niMciii-  i.irre;   d,   the  heads  all   united  in  the  cells  from  which 

tails;  e,  end-piece    ,1  ,1        ,    «i  •      ,« 

of  the  tail.  they  arise,  the  tails  projecting 

the  cavity  of  the  tube.     Bu; 
separated.     They  then  consist  of  a  head  and  a 


THE   URETHRA.  279 


In  length  they  are  about  ^th  to  -A^th  of  an  inch.  The 
head  is  somewhat  elliptical  and  the  tail  gradually  tapers.  In 
other  animals  than  man  the  size  and  form  vary  from  those 
of  man,  though  in  a  general  way  they  conform. 

There  is  a  very  active  vibratory  motion  of  the  tail  of  the 
spermatozoon,  which  allows  it  quite  free  motion  in  a  fluid 
medium.  It  is  by  this  swimming  motion,  in  which  it  may  be 
compared  to  a  tadpole,  that  the  seminal  cell  is  able  to  reach 
the  ovum  against  the  action  of  the  cilia  in  the  uterus  and  Fal- 
lopian tube. 

Seminal  vesicles  :  They  are  tubules  which  join  the  vasa 
deferentia,  and  lie  upon  the  base  of  the  bladder,  emptying 
into  the  urethra  by  the  ejaculatory  ducts  through  the  prostate 
gland.  In  structure  the  vesiculse  seminales  are  convoluted  and 
dendritic.  They  are  lined  by  a  mucous  membrane  and  are  con- 
voluted and  folded  so  as  to  present  a  sacculated  appearance. 

Prostate  gland  :  It  is  a  gland  lying  at  the  base  of  the 
bladder  and  surrounding  the  urethra  at  its  beginning.  It  has 
the  general  structure  of  the  glandular  organs,  and  in  addi- 
tion a  considerable  amount  of  muscular  tissue.  Its  acini 
empty  into  ducts  which  empty  into  the  urethra.  Its  function 
is  not  exactly  known. 

The  penis  consists  of  three  more  or  less  cylindrical  bodies 
of  erectile  tissue  enclosed  in  fibrous  sheaths.  The  two  cor- 
pora cavernosa  lie  above,  and  receive  between  them,  below, 
the  corpus  spongiosum,  in  which  the  urethra  is  contained. 
The  glows  penis  is  continuous  with  the  corpus  spongiosum. 
The  covering  of  the  penis  is  of  loose  skin,  but  over  the  glans 
penis  and  lining  the  prepuce  it  resembles  mucous  membrane. 
In  this  region  there  is  an  abundant  subcutaneous  nerve- 
plexus,  and  the  Pacinian  bodies  are  quite  numerous,  so  that 
it  is  possessed  of  acute  sensibility. 

The  urethra  extends  from  the  bladder  through  the  corpus 

spongiosum  to  the  end  of  the  penis.      It  is  lined  with  mucous 

membrane,  and  is  furnished  in  its  deeper  layers  with  numer- 

ous muscular  fibres.     There  are  a  number  of  ducts  of  glands 

it  whose  function  is  not  fully  understood,  though 

m  is  supposed  to  be  added  to  that  of  the  seminal 

nake  up  the  semen. 


280  REPROD  UCTION. 

Erectile  tissue  of  the  penis  :  The  erectile  tissue  consists  of  a 
system  of  distensible  vacuoles  containing  venous  blood,  lying 
in  the  interstices  of  a  fibrous  connective  tissue.  The  erector 
penis  muscle  by  its  contraction  compresses  the  veins  of  the 
organ,  and  the  veins  become  turgid  with  blood.  The  arteries 
enter  the  structure  of  the  erectile  tissue  along  the  pubic 
bone,  and  are  not  pressed  upon  by  the  contraction  of  the 
muscle. 


Impregnation  in  the  Human  Species. 

Impregnation,  or  fecundation,  are  the  terms  applied  to  the 
junction  of  the  male  and  female  elements  (spermatozoon  and 
ovum),  by  virtue  of  which  the  joined  elements  become  one, 
and  by  developmental  growth  eventually  become  an  indi- 
vidual of  the  species.  If  no  junction  of  sperm atazoon  and 
ovum  takes  place,  each  dies  and  is  cast  off.  If,  however,  the 
ovum  is  fertilized  by  the  spermatazoon,  a  new  life  is  begun. 

Methods  of  fertilization  :  The  methods  by  which  the  male 
spermatazoon  and  ovum  are  brought  in  contact  vary  for  dif- 
ferent classes  of  animals.  As  has  already  been  mentioned, 
in  some  classes  of  fishes  the  female  ejects  her  spawn  and  the 
male  his  elements,  at  different  places,  and  owing  to  the  ocean 
currents  the  male  elements  are  brought  into  contact  with  the 
female  elements.  In  frogs  the  male  fertilizes  the  ova  just  as 
the  latter  leave  the  female.  In  mammalia  the  male  intro- 
duces the  spermatozoa  into  the  genital  passages  of  the  female, 
and  this  act  is  called  coitus. 

Coitus :  The  act  of  coitus  is  preceded  by  a  preliminary 
period  of  sexual  excitement,  more  marked  in  the  male,  during 
which  the  penis  becomes  swollen,  turgid,  and  erect.  The 
penis  is  then  introduced  into  the  female  vagina.  As  a  result  of 
muscular  movements  there  is  friction  upon  the  delicate  sen- 
sory nerve  end-organs  of  the  glans  penis  and  clitoris,  pro- 
ducing intense  nervous  sensations,  leading  finally  to  a  climax 
of  excitement  on  the  part  of  both  male  and  female  that 
gradually  fades  away.  During  the  climax  (or  orgasm)  there 
is  an  ejaculation  <>i'  seminal  fluid  on  the  part  of  the  male 
into  the  upper  end  of  the  vagina  of  the  female.  There 


DETAILS  OF  IMPREGNATION.  281 

is  also  a  flow  of  secretion  from  the  glands  of  Bartolini  of  the 
female,  and  also,  presumably,  a  rhythmical  opening  and  clos- 
ing of  the  cervical  canal. 

Site  of  impregnation  :  Although  the  seminal  fluid  of  the  male 
is  lodged,  at  the  close  of  coitus,  in  the  vagina  of  the  female,  the 
spermatozoa  are  not  yet  in  contact  with  the  ovum.  By  virtue 
of  their  inherent  mobility  the  spermatozoa  travel  along  the 
cervical  canal  into  the  cavity  of  the  uterus,  there  to  meet  the 
ovum.  The  spermatozoa  may  even  travel  along  the  Fallo- 
pian tubes,  impregnating  the  ovum  in  the  lumen  of  the  tube ; 
or  may  even  leave  the  tubes  by  their  fimbriated  ends  and 
impregnate  the  ovum  on  the  surface  of  the  ovary. 

Time  of  impregnation :  Probably  immediately  before  the 
menstrual  period ;  but  owing  to  the  fact  that  both  the  female  and 
the  male  elements  may  remain  in  the  genital  passages  of  the 
female  for  some  days  in  a  healthy  condition,  it  is  difficult  to 
fix  the  time  of  actual  impregnation  of  the  ovum. 

Impregnation  is  generally  supposed  to  occur  a  short  time 
before  menstruation,  on  the  following  grounds : 

(1)  It  is  probable  that  in  most  instances  the  rupture  of  the 
Graafian  follicle  occurs  just  before  the  menstrual  period.  (2) 
The  uterus  is  in  the  most  favorable  condition  to  sustain  the 
fecund  ovum  at  that  time,  because  of  the  presence  of  the 
decidua  menstrual  is.  (3)  Among  the  Jews,  a  remarkably 
prolific  race,  coitus  is  prohibited  by  the  religious  law  for  a 
week  after  menstruation. 

Details  of  impregnation  :  The  spermatozoon  travels  along 
the  uterus  or  Fallopian  tubes  until  it  comes  in  contact  with 
the  ovum.  The  spermatozoon,  by  lashing  its  tail,  wriggles 
through  the  zona  radiata  (pellucida)  of  the  ovum  and  enters 
the  perivitelline  space.  Several  spermatozoa  may  succeed  in 
effecting  an  entrance  as  far  as  the  perivitelline  space ;  but  be- 
yond this,  for  some  unknown  reason,  but  one  spermatozoon 
goes  further  and  enters  the  vitellus  proper ;  the  others  die. 
The  spermatozoon  destined  to  fertilize  the  ovum  now  loses  its 
tail,  and  the  head  and  centre-piece  are  called  the  male  pro- 
nucleus.  The  male  pronucleus  and  female  pronucleus  now 
fuse  together  in  the  centre  of  the  egg  and  form  the  first  seg- 
mentation-nucleus. 


DEVELOPMENT. 

On  the  formation  of  the  first  segmentation-nucleus  the  act 
of  imi>r<-<iiniti<ni  is  complete,  and  the  subsequent  changes  in 
the  growth  of  the  ovum  come  under  the  head  of  "  Develop- 
ment," 

DEVELOPMENT. 

Methods  of  study  of  development :  The  early  development 
of  the  human  ovum  has  not  been  studied  with  accuracy,  but 
we  have  reasoned  by  analogy,  from  observations  upon  the 
lower  animals.  One  method  is  to  watch  the  changes  in  the 
development  of  the  egg  of  the  common  fowl.  This  is  on 
account  of  the  accuracy  with  which  the  time  of  development 
inav  be  watched,  and  the  convenience  to  the  observer  of  such 
simple  growth  by  incubation  compared  with  uterine  growth. 
The  processes  of  development  are  not  materially  different. 

Segmentation :  The  most  frequent  site  of  impregnation  is 
probably  the  Fallopian  tubes,  and  while  there  the  ovum  re- 
ceives a  layer  of  clear  albuminous  material,  which  adds  con- 
siderably to  its  bulk.  This  corresponds  to  the  white  of  a 
hen's  egg. 

The  next  change  which  occurs  in  the  impregnated  eg<r  is 
the  splitting  up  of  the  vitellus  or  yelk,  first  in  halves,  then 
in  quarters,  and  so  on  until  the  vitellus  becomes  a  mass  of 
minute  granular-looking  nucleated  cells  (Fig.  139).  The 
segmentation  of  the  nucleus  precedes  and  continues  with  the 
corresponding  change  in  the  yelk. 

Germinal  membrane:  After  the  yelk  has  subdivided  into  a 
large  number  of  cells  these  cells  undergo  a  centrifugal  action, 
with  the  result  that  they  form  a  complete  inner  lining  for 
the  /ona  pellucida  of  closely  packed  polygonal  cells,  leaving 
a  central  clear  cavity  containing  the  vitelline  liquid.  This 
lining  is  the  germinal  or  blastodermic  membrane. 

Site  of  segmentation :  So  far  the  ovum  has  probably  re- 
mained in  the  Fallopian  tube,  but  now  descends  into  the 
uterus.  The  descent  into  the  uterus  is  estimated  to  take 
place  about  ten  days  after  impregnation. 

Before  studying  the  subsequent  development  of  the  blasto- 
tli-nn.  let  ii-  see  what  changes  have  taken  place  in  the  lining 
of  the  uterus  to  prepare  it  for  the  reception  of  the  ovum. 


CHANGES  IN  THE  BLASTODERM. 


283 


Changes  in  the  uterine  lining :  The  decidua  menstrualis  has 
been  mentioned  as  specially  suitable  for  the  reception  of  the 
ovum.  But  if  impregnation  occur,  it  is  not  called  by  this 
name,  as  menstruation  does  not  occur.  It  is  then  known  as 
the  decidua  vera.  It  consists  of  a  thick,  succulent  mucous 
membrane  caused  by  the  proliferation  of  the  subepithelial 
cells.  Into  this  decidua  the  ovum  falls,  and  its  shaggy 
chorion  implants  its  villi  in  the  crypts  of  the  mucous  mem- 

FIG.  139. 


Segmentation  of  the  vitellus  in  the  impregnated  egg  of  the  rabbit  (Coste). 

brane.  The  decidua  soon  envelops  it,  and  the  portion  which 
is  reflected  over  the  ovum  is  known  as  the  decidua  reflexa. 

Changes  in  the  blastoderm :  There  appears  at  one  point  an 
opaque  streak  (Fig.  140),  which  is  found  to  be  due  to  the 
proliferation  of  the  cells  of  the  blastoderm.  This  is  the 
primitive  trace,  and  it  grows  in  length  and  breadth. 

The  surrounding  area  of  increased  cell-proliferation  is 
called  the  "  area  germinativa."  The  blastoderm — ?.  e.,  that 
portion  or  area  of  the  blastodermic  membrane  in  which  the 
embryo  is  actually  developing — increases  in  area  from  the 
rapid  proliferation  of  cells,  and  folds  up  at  each  end  trans- 


284  DEVELOPMENT. 

versely  and  at  the  sides  longitudinally.  These  folds  are 
of  great  importance,  for  it  is  in  this  way  that  the  contour 
of  the  body  is  outlined,  and  if  it  were  not  for  them  the 
blastoderm  would  continue  to  develop  as  a  flat  surface. 
The  transverse  folds  are  at  each  end,  and  are  known  as 
the  head  and  tail  folds.  The  longitudinal  folds  define  the 
outlines  of  the  body  (see  Amnion).  There  also  occurs  a  con- 
striction of  the  entire  ovum ;  above  the  constriction  is  the 
developing  embryo,  and  below  the  constriction  is  the  yelk-sac 
(see  page  287).  Together  with  these  changes  the  cells  of  the 

FIG.  140. 


Diagram  of  the  area  germinativa,  showing  the  primitive  trace  and  area  pellucida. 

blastoderm  and  blastodermic  membrane  split  up  into  three  con- 
centric layers — the  epiblast,  mesoblast,  and  hypoblast  (Fig.  141); 
and  along  the  axis  of  the  primitive  trace  a  groove  is  formed 
which  is  destined  to  become  the  cerebro-spinal  axis.  This  is 
the  primitive  groove,  or  medullary  groove. 

Development  of  the  medullary  groove  :  Certain  ridges  or  folds 
appear  in  the  epiblast  on  either  side  (mesial  to  and  smaller 
than  the  ones  mentioned  above).  They  continue  to  thicken, 
and  finally  coalesce  dorsally,  leaving  a  lining  of  cells  within 
a  tube.  These  cells  develop  the  cerebro-spinal  axis  (cord  and 
brain)  and  follow  the  curves  of  the  blastoderm  longitudinally. 
It  is  to  be  noticed  that  the  enclosure  of  the  spinal  canal  in 


STRUCTURES  DERIVED  FROM  THE  MESOBLAST.      285 

this  way  is  by  a  folding  process,  and  all  through  the  process 
of  development  this  peculiarity  is  very  marked. 

Meanwhile  the  mesoblast  has  developed  a  number  of  proc- 
esses, which  become  a  primitive  spinal  column. 


Section  of  a  blastoderm  at  right  angles  to  the  long  axis  of  the  embryo,  near  its 
middle,  after  eight  hours'  incubation  (from  Foster  and  Balfour).  A,  epiblast 
formed  of  two  layers  of  cells ;  B,  mesoblast,  thickened  below  the  primitive 
groove;  C,  hypoblast,  formed  of  one  layer  of  flattened  cells;  pr,  primitive 
groove  ;  me,  mesoblast  cell ;  bd,  formative  cells  in  the  so-called  segmentation  or 
subgerminal  cavity  (the  line  of  separation  between  the  epiblast  and  mesoblast 
below  the  primitive  groove  is  too  strongly  marked  in  the  figure). 

Changes  in  the  mesoblast :  The  mesoblast  throughout  a  por- 
tion of  its  distance  subdivides  into  two  layers,  one  part  of  the 
split  mesoblast  adhering  to  the  epiblast,  while  the  remainder 
joins  the  hypoblast.  The  former  is  known  as  the  somato- 
pleure,  and  the  latter  as  the  splanchnoplture,  and  the  included 
space  becomes  the  pleuro-peritoneal  cavity,  which  subse- 
quently divides  and  diiferentiates  to  form  the  pleural,  pericar- 
diac,  and  peritoneal  cavities. 

Structures  derived  from  the  epiblast :  The  epiblast  develops 
into  the  epidermis  and  appendages  of  the  skin,  the  great 
nervous  centres,  the  nerves,  and  the  principal  portions  of  the 
organs  of  special  sense — eye,  ear,  nose. 

Structures  from  the  mesoblast :  The  bones,  muscles,  fasciae, 
and  connective  tissues  of  the  body.  It  also  develops  the 
vascular  stem.  It  must  be  remembered  that  very  early  in 
embryonal  life  this  tissue  divides  to  join  with  the  epiblast  and 
hypoblast,  and  we  can  therefore  understand  how  it  may  de- 
velop the  muscular  structures  of  the  intestinal  canal. 


286  DEVELOPMENT. 

Structures  from  the  hypoblast :  The  epithelial  elements  of  the 
glands  and  the  mucous  membranes  lining  the  alimentary  and 
pulmonary  tracts. 

Destiny  of  the  splanchnopleure  :  The  splanchnopleure  (6',  Fig. 
142)  folds  in  over  the  remainder  of  the  ovum,  and  so  walls 
in,  so  to  speak,  the  yelk-sac,  which  communicates  freely  with 
the  interior  of  the  embryo.  Later  on,  after  the  formation 
of  the  amnion,  the  yelk-sac  forms  a  blind  pouch  which  is 
lined  with  hypoblast  and  has  an  external  covering  of  meso- 
blast,  as  is  shown  at  6  in  the  accompanying  cut.  The  upper  6 


Transverse  sections  through  the  embryo  chick,  before  and  some  time  after  the 
closure  of  the  medullary  canal,  to  show  the  upward  and  downward  inflections 
of  the  blastoderm  (after  Remak)  on  the  third  day  in  the  lumbar  region.  1,  noto- 
chord  in  its  sheath  ;  2,  medullary  canal,  now  closed  in ;  3,  section  of  the  medul- 
lary substance  of  the  spinal  cord ;  4,  epiblast ;  5,  somatopleure  of  the 
mesoblast;  5',  splanchnopleure  (the  figure  is  placed  in  the  pleuro-peritnneal 
cavity);  6,  layers  of  hypoblast  in  the  intestines,  spreading  also  over  the  yelk; 
4x5,  part  of  the  fold  of  the  amnion  formed  by  the  epiblast  and  somatopleure. 

is  in  the  primitive  gut,  which  derives  its  epithelial  elements 
from  the  hypoblast  and  its  muscular  and  serous  coverings 
from  the  mesoblast. 

Umbilical  vesicle :  After  the  constriction  of  the  vitellus  or 
ovum  (page  285),  separating  the  main  portion  of  the  vitellus 
from  the  cavity  of  the  future  alimentary  tract,  the  con- 
stricted portion,  or  tube,  is  known  as  the  "vitelline  duct," 
and  the  rest  of  the  vitellus  is  called  the  "  umbilical  vesicle," 
both  at  an  earlier  period  of  development  being  known  as  the 
ydk-tnc. 

From  the  latter  the  embryo  derives  its  sustenance  in  the 


PURPOSE  OF  THE  AMNION. 


287 


earlier  stages.  Early  in  the  development  bloodvessels  begin 
to  form,  and  they  ramify  over  the  surface  of  the  umbilical 
vesicle  and  help  to  absorb  its  contents. 

Amnion  :  While  one  portion  of  the  split  mesoblast  (splanch- 
nopleure)  unites  with  the  hypoblast  to  form  the  splanchnoblast 
and  alimentary  organs,  the  outer  layer  (somatopleure)  and 
epiblast  are  united  to  form  the  skin  and  walls  of  the  body  as 
the  somatoblast.  The  somatoblast  now  folds  up  and  around 
the  embyro,  above  and  lateral  to  the  folds  of  the  medullary 
groove  already  mentioned.  It  must  be  remembered,  however, 
that  the  entire  globe  of  the  ovum  is  invested  by  the  somato- 
blast, and  that  in  folding  up  in  this  way  its  cells  are  in  a 


Diagram  of  the  fecundated  egg,  farther 
advanced,  a,  umbilical  vessel ;  b, 
amniotic  cavity,  not  yet  complete ; 
c,  allantois. 


Diagram  of  the  fecundated  egg,  with 
allantois  nearly  complete,  a,  inner 
lamina  of  amniotic  fold ;  6,  outer 
lamina  of  amniotic  fold;  c,  point 
where  the  amniotic  folds  come  in 
contact.  The  allantois  is  seen  pene- 
trating between  the  inner  and  outer 
laminae  of  the  amniotic  folds. 


measure  raised  away  from  the  splanchnoblast.  This  "  rais- 
ing away  "  is  further  aided  by  the  sinking  of  the  embryo.  The 
layers  of  the  somatoblast  fold  up  until  they  meet  and  unite 
behind  the  embryo,  and  in  this  way  form  a  layer  of  membrane 
which  lines  the  ovum  and  another  layer  which  encloses  the 
embryo  (Fig.  143).  This  latter  layer  forms  the  true  amnion. 
(This  is  better  understood  by  reference  to  the  cuts.) 

Purpose  of  amnion :  It  covers  the  embryo  in  the  early  stages 
very  closely ;  but  soon  becomes  distended  with  a  pale  watery 
fluid,  which  serves  to  float  the  foetus  and  give  it  equal  me- 


288  DEVELOPMENT. 

chanical  support  on  all  sides.     The  outer  layer  of  the  amnion 

becomes  very  thin  and  adheres  to  the  chorion. 

The   amniotic  fluid   consists  of  water  containing  a  small 

amount  of  albumin,  urea  and  salt. 

Allantois :    During  the  development  of  the   amnion    from 

the  somatoblast  a  change  has  occurred  in  the  splanchnoblast. 
From  near  the  caudal  extremity  of 
the  primitive  gut  there  has  budded 
a  small  mass  which  develops  rap- 
idly, following  the  outline  of  the 
amnion  (see  Figs.  143,  144,  14")), 
and  grows  fast  to  its  chorion  layer. 
This  structure,  the  allantois,  soon 
becomes  very  vascular  and  carries 
its  bloodvessels  to  the  chorion. 

Purpose  of  the  allantois :  It  nourishes 
the  growing  embryo.     The   chorion 

Diagram   of  the    fecundated      /          ii\il          IJT_  i>      i 

iw.  with  the  allantois  luiiy     (see  below)  has  already  become  tutted 

Sm^'SjSi     with  capillary  loops,  and  has  estab- 

lished  a  connection  with  the  decidua 

of  maternal  growth.  As  the  vessels  of  the  allantois  communi- 
cate more  and  more  with  the  chorion,  the  embryo  derives 
more  of  its  sustenance  from  the  mother,  and  the  remains  of 
the  yelk-sac  (umbilical  vesicle)  dwindle  as  the  need  is  less 
and  the  substance  is  consumed  (see  Figs.  143,  144,  145). 
Subsequent  history  of  the  allantois :  After  the  development 
of  the  placenta  the  allantois  dwindles  away,  all  except  the  por- 
tion nearest  the  foetus ;  this  becomes  the  urinary  bladder  and 
the  urachus  (the  latter,  in  the  adult,  is  an  impervious  cord 
extending  from  the  bladder  to  the  umbilicus). 

Chorion :  the  chorion  is  the  outer  zone  of  the  ovum,  and 
from  its  surface  there  project  centrifugally  a  large  number  of 
villi. 

The  chorion  consists  of  several  layers  which  fuse  into  one 
vascular  membrane:  the  allantois,  the  outer  layer  of  the 
amnion,  and  the  vitelline  membrane  are  united  in  the  chorion. 
As  the  embryo  develops  the  vessels  of  the  chorion  become 
thinner  on  the  side  toward  the  uterine  cavity,  and  more  dis- 
tinct on  the  opposite  side.  This  change  continues  as  the 


ASSOCIATION  OF  FCETAL  AND  MATERNAL  BLOOD.     289 

embryo  increases,  until  the  placenta  is  formed  by  the  branch- 
ing of  the  embryonic  vessels  and  the  increase  of  the  decidua 
at  the  corresponding  point. 

Association  of  decidua  and  chorion :  In  the  deeper  part  of 
the  mucous  membrane  of  the  uterus,  at  the  implantation  of  the 
chorion,  there  are  hollowed-out  spaces  or  sinuses  in  the  tissues, 
which  communicate  both  with  a  maternal  vein  and  an  artery — 
that  is,  special  arrangements  are  made  for  the  rapid  circula- 
tion of  a  large  amount  of  blood  in  the  uterine  mucous  mem- 
brane at  the  placental  site.  At  the  same  time  the  glandular 
structures  of  the  uterine  mucous  membrane  are  increased,  and 
the  follicles  run  deeply  into  the  thick  and  succulent  tissues. 

The  villi  dip  down  and  develop  new  tufts  of  capillaries  in 
the  deepened  crypts  of  mucous  membrane,  so  that  the  tufts 
of  capillaries  of  the  chorion  may  be  said  to  resemble  in  a 
way  a  glove  filled  with  foetal  blood  dipping  into  a  vessel  filled 
with  maternal  blood. 

The  placenta  :  So  far  the  villi  throughout  the  entire  surface 
of  the  ovum  become  associated  with  the  decidua.  Now,  as 
development  advances,  that  portion  of  the  chorionic  villi  that 
is  lined  by  the  central  portion  of  allantois  grows  still  further 
in  size,  while  the  rest  of  the  chorionic  villi  atrophy  and  disap- 
pear. The  loops  of  bloodvessels  of  the  allantois  project  into 
the  villi  of  the  chorion  (like  a  finger  into  a  glove),  and  thus 
are  brought  into  closer  contact  with  the  blood  of  the  decidua 
(maternal  blood).  The  portion  of  villi  of  chorion  containing 
the  vessels  of  the  allantois  is  the  placenta. 

Thus  we  see  that  the  placenta  consists  really  of  two  parts 
— a  foetal  portion,  consisting  of  fcetal  bloodvessels  contained 
in  the  chorionic  villi ;  and  a  maternal  portion,  consisting  of 
follicles  or  depressions  in  the  uterine  wall,  surrounded  by 
bloodvessels  so  enlarged  as  to  form  blood-chambers  (uterine 
sinuses).  The  chorionic  villi  are  lodged  in  the  uterine  follicles, 
or  between  the  follicles,  according  to  some  observers. 

Association  of  foetal  and  maternal  blood :  The  foetal  blood 
never  comes  directly  in  contact  with  the  maternal  blood. 
The  two  blood-currents  are  nearest  each  other  while  circulat- 
ing through  the  placenta. 

While  in  the  placenta  there  are  four  layers  of  cells  between 

19— Phys. 


290  DEVELOPMENT. 

the  maternal  and  the  foetal  blood  :  1,  wall  of  chorion  capil- 
lary;  2,  cells  of  chorion;  3,  cells  of  uterine  follicle;  and  4, 
wall  of  the  uterine  sinus. 

Interchange  between  foetal  and  maternal  blood :  Although 
there  is  no  direct  communication  between  the  blood  of  the  foetus 
and  that  of  the  mother,  nevertheless  while  passing  through 
the  placenta  there  is  an  exchange  by  osmosis  between  the 
mother's  blood  and  the  foetal  blood. 

The  mother's  blood  furnishes  to  the  foetal  blood  food  and 
oxygen,  and  in  turn  removes  the  carbonic  acid  and  excre- 
mentitious  material  which  the  foetus  must  lose — that  is,  the 
placental  circulation  supplies  the  place  taken  in  after-life  by 
the  alimentary  and  the  respiratory  tracts. 

Umbilical  cord :  The  umbilical  cord  or  funis  is  the  stalk 
connecting  the  placental  with  the  foetus,  and  its  purpose  is  to 

l>e  a  framework  or  support  for  the 
Fro.  146.  umbilical  arteries  and  veins.     The 

tissues  of  the  umbilical  cord  are 
formed  from  the  vascular  allantois, 
which  carries  the  arteries  and  veins. 
It  also  has  an  external  coating 
of  the  amnion  and  the  shrivelled 
umbilical  vesicle  and  its  duct  (Fig. 
146).  How  this  occurs  will  readily 
be  seen  by  reference  to  the  accom- 
panying cut. 

Human  embryo  and  its  envel-  \,       n 

opes  at  the  end  of  the  third  At      Iirst      two     arteries     COI1VCV 

SenfoV'Smnio1;'  6nlarge"    the    blood   from    the  foetus   to   the 
placenta,    and     two    veins     carry 

the  purified  blood  from  the  placenta  to  the  foetus.  Later  on 
in  foetal  life  one  of  the  veins  is  lost.  At  term  the  umbilical 
cord  is  a  rope-like  structure  between  18  inches  and  36  indies 
long,  and  consists  of  one  vein  and  two  arteries  spirally  twisted ; 
the  vessels  are  enclosed  in  a  layer  of  jelly-like  substance 
(Wharton's  jelly),  and  the  whole  is  surrounded  by  a  con- 
nective-tissue sheath.  The  cord  is  about  one-half  inch  in 
diameter. 

Destiny  of  placenta  :  The  foetal  part  is  almost  all,  excepting 
some  of  the  capillary  tufts  which  are  torn  off,  discharged  in 


PLACENTAL   CIRCULATION.  291 

the  after-birth  ;  but  the  decidua  is  not  entirely  disposed  of  in 
this  way,  the  portions  remaining  being  in  part  absorbed  and 
in  part  found  in  the  lochia  which  occur  for  a  fe\v  days  after 
the  birth. 

When  the  placenta  is  expelled  a  part  of  the  maternal 
tissue  is  left  behind,  and  there  is,  of  course,  a  loss  of  the 
blood  contained  in  the  uterine  sinuses,  but  the  general  bal- 
ance of  the  circulation  is  not  disturbed  at  childbirth.  The 
reason  for  this  is  the  oblique  entrance  of  the  placental  vessels. 
They  enter  the  sinuses  at  an  angle,  and  are  therefore  com- 
pressed by  the  muscular  tissue  of  the  uterus  in  its  contracted 
state. 

Appearance  of  placenta :  The  placenta  at  term  appears  as  a 
thick,  cake-like  disk  of  vascular  tissue.  Its  maternal  and 
foetal  portions  are  so  intermingled  that  they  cannot  be  sepa- 
rated. In  size  it  covers  about  one-third  of  the  uterine 
wall. 

Period  of  placental  formation :  The  placenta  is  formed  at 
about  the  third  month  of  pregnancy.  Before  that  time  the 
chorion  is  covered  by  the  decidua  reflexa  and  nourishes  the 
embryo,  but  as  the  placenta  becomes  more  developed  other 
parts  of  the  chorion  atrophy. 

Foetal  Circulation. 

Types  of  foetal  circulation :  One  meets  with  two  distinct 
types  of  circulation  in  foetal  life  :  the  vitelline  circulation  and 
the  placental  circulation.  In  both  types  the  blood  is  the  circu- 
lating medium  driven  on  by  the  heart,  the  essential  difference 
being  the  site  where  the  foetal  blood  is  enriched.  The  vitel- 
line circulation  precedes  that  of  the  placenta,  and  as  soon  as 
the  latter  is  formed  the  former  disappears. 

Vitelline  circulation  :  In  the  vitelline  circulation  the  vessels 
from  the  foetus  (omphalo-mesentric  vessels)  pass  over  the 
yelk-sac  and  carry  nutrition  to  it  from  the  growing  organism. 
The  vitelline  circulation  in  the  human  ovum  is  not  very  long- 
lived,  for  the  chorion  is  early  formed  and  the  stock  of  nutri- 
ent protoplasm  in  the  yelk-sac  is  very  small. 

Placental  circulation :  In  the  placental  circulation  the  foetal 


292 


DEVELOPMENT. 


blood  is  purified  and  enriched  by  osmosis  with  the  maternal 
blood  in  the  placenta. 

Development    of  circulatory  apparatus :  Among  the  earliest 
changes  in  the  blastoderm,  occurring  in  the  second  week  of 
impregnation,  is  the  formation   of  bloodvessels  and  blood- 
corpuscles.      This   occurs   by    the   proliferation    of    certain 
branched  cells  of  the  mesoblast,  and 
FIG.  147.  these  cells  form  a  closed  system  of 

branching  capillaries,  their  nuclei 
acquiring  a  red  color  and  becoming 
the  blood-corpuscles.  This  area  is 
external  to  but  connected  with  the 
embryo,  and  is  known  as  the  "  area 
vasculosa." 

The  area  vasculosa  extends  all 
about  the  blastoderm  upon  the  sur- 
face of  the  vitellus,  and  as  the  folds 
of  the  embryo  occur  the  vessels  are 
brought  to  enter  the  body  through 
the  space  at  which  the  vitellus  is  shut 
in  to  form  the  primitive  gut.  There 
are  then  two  arteries  and  two  veins 
which  are  known  as  the  omphalo- 
mesenteric  vessels.  This  form  of 
circulation  soon  gives  way  to  the  placental,  and  the  vessels 
passing  to  the  umbilical  vesicle  waste,  those  belonging  to  that 
portion  of  the  original  vitelline  cavity  which  forms  the  intes- 
tine, becoming  the  mesenteric  vessels. 

Formation  of  heart :  About  the  time  of  the  formation  of 
the  area  vaseulosa  certain  cells  of  the  visceral  layer  of  the 
incsoblast  (splanchnopleure)  develop  a  tube  upon  each  side  of 
the  body,  and  these  two  tubes  soon  coalesce  to  form  a  single 
tube  (Fig.  148),  which  receives  two  veins  at  its  lower  end  and 
gives  off  two  arteries  at  its  upper.  This  is  the  primitive 
heart,  and  pulsations  begin  in  it  very  feebly  almost  as  soon 
as  there  is  a  trace  of  the  originating  cells.  This  structure 
soon  develops  a  muscular  tissue  and  a  circulating  fluid  which 
shortly  presents  the  character  of  blood. 

The  heart  then  bends  on  itself  so  as  to  assume  a  U-shape, 


Diagram  of  embryo  and  its 
vessels,  showing  the  circu- 
lation of  the  umbilical  ves- 
icle, and  also  that  of  the 
allantois,  beginning  to  be 
formed. 


COURSE  OF  THE  FCETAL   CIRCULATION. 


293 


which  shortly  is  twisted  in  such  manner  that  the  arterial  end 
of  the  heart  crosses  in  front  of  the  venous  (Fig.  149),  and 
the  loop  suggests  the  outline  of  the  ventricles. 

In  the  next  stage  of  development  the  septum  between  the 
ventricles  grows,  and  separates  the  heart  into  two  divisions  ; 
and  at  about  the  same  time  the  auricles  are  developed  and 
the  valves  become  well  marked.  These  changes  occur  in  the 
fourth  to  the  eighth  week  of  embryonic  life. 


FIG.  148. 


FIG.  149. 


FIG.  150. 


FIG.  148.— Earliest  form  of  the  foetal  heart.  1,  venous  extremity;  2,  arterial  ex- 
tremity. 

FIG.  149.— Foetal  heart  bent  upon  itself.   1,  venous  extremity ;  2,  arterial  extremity. 

FIG.  150.— Foetal  heart  still  further  developed.  1,  aorta;  2,  pulmonary  artery;  3,3, 
pulmonary  branches ;  4,  ductus  arteriosus. 

Characteristics  of  placental  circulation :  After  the  cessation 
of  vitelline  circulation  the  needs  of  the  fetus  are  supplied  by 
the  placental  circulation  until  birth.  The  placental  circula- 
tion presents  two  prominent  features  in  which  it  diifers  from 
adult  circulation : 

(1)  In  the  arterial  circulation  some  conditions  of  the  heart 
and  great  vessels  are  necessary  to  modify  the  pulmonary  cir- 
culation before  the  air  enters  the  lungs  at  birth.  (2)  In  the 
circulation  of  the  liver  the  veins  present  modifications  to 
allow  for  the  return  placental  circulation. 

Course  of  foetal  circulation :  Ductus  venosus :  The  foetal 
blood,  purified  and  enriched  in  the  placenta,  passes,  by  the 
umbilical  vein  in  the  umbilical  cord,  to  the  umbilicus.  The 
umbilical  vein  then  courses  from  the  umbilicus  to  the  under 
surface  of  the  liver ;  here  the  vein  divides  into  two  parts. 
One  portion  of  the  blood  enters  into  the  liver-substance, 
and  after  traversing  its  capillaries  is  poured  out  by  the  hepatic 


294  DEVELOPMENT. 

veins  into  the  inferior  vena  cava.  The  other  portion  of 
blood  passes  directly  from  the  umbilical  vein  into  the  inferior 
vena  cava  by  means  of  a  blood-channel,  the  ductus  venom n*. 

Foramen  ovale :  The  blood  in  the  vena  cava  inferior  empties 
into  the  right  auricle  of  the  foetal  heart.  Instead  of  passing 
from  the  right  auricle  into  the  right  ventricle,  as  is  the  case  in 
the  adult  circulation,  the  blood  from  the  inferior  vena  cava 
passes  from  the  right  auricle  into  the  left  auricle  by  means 
of  an  opening  in  the  interauricular  septum.  The  opening  is 
called  the  "foramen  ovale"  The  flow  of  blood  from  the 
inferior  vena  cava  through  the  foramen  ovale  and  into  the 
left  auricle  is  facilitated  by  the  fact  that  the  inferior  vena 
cava  points  almost  directly  into  the  foramen  ovale. 

The  Eustachian  valve  also  favors  this  peculiar  course  of  the 
blood.  The  Eustachian  valve  consists  of  a  crescentic  fold  of 
fibrous  tissue  covered  with  endocardium.  The  fold  extends 
from  a  point  between  the  opening  of  the  superior  and  inferior 
venae  cavse  over  to  the  lower  and  anterior  margin  of  the  fora- 
men ovale.  The  base  of  the  fold  lies  on  the  right  auriculo- 
ventricular  ring,  and  the  concavity  of  the  fold  is  directed 
upward.  From  its  position  the  Eustachian  valve  acts  as  a 
guiding-groove  or  gutter  for  passing  the  blood  from  the  in- 
ferior vena  cava  to  the  foramen  ovale. 

Ductus  arteriosus :  On  entering  the  left  auricle,  the  blood 
is  passed  into  the  left  ventricle  and  thence  into  the  aorta,  to 
be  distributed  all  over  the  body  ;  but  principally  to  the  head 
and  upper  extremities. 

The  blood  from  the  head  and  upper  extremities  returns  to 
the  heart  by  the  superior  vena  cava.  On  entering  the  right 
auricle  the  blood  from  the  superior  vena  cava  passes  in  front 
of  the  stream  that  flows  from  the  inferior  vena  cava  to  the 
foramen  ovale,  and  enters  the  right  ventricle. 

The  direction  in  which  the  superior  vena  cava  points  (to- 
ward the  auriculo-ventricular  ring),  and  also  the  Eustachian 
valve,  arc  the  factors  that  determine  the  separation  of  these 
two  streams.  On  entering  the  right  ventricle  the  blood  from 
the  superior  vena  cava  is  forced  into  the  pulmonary  artery 
toward  the  lungs.  Before  reaching  the  lungs  this  blood  meets 
with  a  channel  of  communication  between  the  pulmonary 


EFFECTS  OF  FCETAL   CIRCULATION.  295 

artery  and  the  aorta.  Into  this  channel  (ductus  arteriosus) 
the  larger  portion  of  the  blood  in  the  pulmonary  artery  enters 
and  mingles  with  the  blood  of  the  aorta ;  the  remainder 
passes  along  the  pulmonary  artery  to  the  structure  of  the 
lungs,  which  it  nourishes,  and  thence  back  to  the  left  auricle 
by  means  of  the  pulmonary  veins. 

Hypogastric,  arteries :  The  blood  in  the  aorta  that  comes 
from  the  left  ventricle  passes,  as  has  been  already  stated, 
largely  to  the  head  and  upper  extremities.  The  blood  in  the 
aorta  that  enters  from  the  ductus  arteriosus  largely  passes  into 
the  descending  aorta. 

On  passing  down  the  descending  aorta,  some  of  the  blood 
enters  the  mesenteric  arteries,  and  thence  back  to  the  venous 
circulation  by  means  of  the  portal  vein  and  the  liver.  Some 
of  the  blood  enters  the  iliac  arteries  and  nourishes  the  lower 
extremities  ;  but  the  major  part  of  the  blood  leaves  the  foetal 
body  by  the  hypogastric  arteries.  The  hypogastric  arteries 
are  branches  of  the  internal  iliacs  and  course  along  the  abdo- 
men to  leave  the  foetal  body  at  the  umbilicus.  On  emerging 
from  the  umbilicus,  the  hypogastric  arteries  change  their 
name,  and  are  now  known  as  the  umbilical  arteries,  and  form 
part  of  the  structure  of  the  umbilical  cord  on  their  way  to 
the  placenta. 

Effects  of  arrangement  of  ftetal  circulation  :  The  liver,  re- 
ceiving the  freshest  blood  (from  the  umbilical  vein),  is  the 
best  nourished  of  all  the  organs  of  the  foetus.  The  result  is 
that  the  foetal  liver  is  vastly  larger  in  proportion  than  the 
adult  liver.  Also  the  circulation  of  the  blood  is  made  more 
perfect,  for  the  branches  of  the  aorta  given  off  to  the  head 
and  upper  extremities  distribute  blood  from  the  inferior  vena 
cava  ;  while  the  ductus  arteriosus,  carrying  the  blood  from 
the  superior  cava  and  right  ventricle,  enters  the  aorta  in  such 
a  way  that  most  of  its  blood  is  sent  to  the  lower  extremities 
and  abdominal  organs  and  umbilical  arteries.  In  this  way  the 
deoxidized  blood  is  sent  back  to  the  placenta  for  the  renewal 
of  its  oxygen.  The  lower  extremities  are  less  well  developed 
than  the  upper.  There  are  probably  two  reasons  for  this  :  (1) 
the  blood  is  less  well  aerated  and  less  nutritious  ;  (2)  the  in- 
ternal iliac  arteries,  giving  off  the  umbilical  arteries,  probably 


296  DEVELOPMENT. 

divert  a  considerable  portion  of  the  blood-supply  of  the  ex- 
ternal iliacs  which  go  to  the  lower  extremities. 

In  addition,  we  note  that,  owing  to  the  ductus  arteriosus, 
only  a  little  blood  goes  to  the  lung-tissues.  The  amount  is 
quite  sufficient  to  keep  up  the  nutrition  of  the  lungs,  and  as 
they  have  no  function  before  birth  they  do  not  need  a  la  rue 
blood-supply. 

Change  from  foetal  to  adult  circulation :  The  respiratory  cen- 
tre in  the  medulla,  which  has  been  quiescent  because  it  has 
been  sufficiently  well  supplied  with  oxygen,  is  awakened  as 
soon  as  the  connection  with  the  uterine  sinuses  is  interrupted. 
As  soon  as  the  supply  of  oxygen  sinks  to  a  certain  point,  an 
impulse  of  inspiration  is  generated,  and  the  infant  breathes 
and  the  lungs  assume  a  condition  of  partial  expansion.  With 
the  diminished  resistance  in  the  expanded  lungs  the  amount 
of  blood  in  the  pulmonary  circulation  increases,  and,  the 
amount  passing  through  the  ductus  arteriosus  diminishing, 
this  is  soon  obliterated.  At  the  same  time,  the  blood  return- 
ing to  the  left  auricle  increases  in  quantity,  and  the  intra- 
auricular  pressure  is  greater;  then,  too,  the  inferior  venacavu 
sends  less  blood,  for  the  ductus  venosus  no  longer  carries  the 
blood  from  the  placental  circulation,  and,  therefore,  the  fora- 
men ovale  is  not  used,  and  is  soon  closed  by  the  adhesion  of 
its  valve-like  curtain.  Thus,  we  have  the  adult  circulation 
established  in  the  place  of  the  foetal  in  consequence  of  the 
respiratory  movements. 

Also,  owing  to  the  division  and  occlusion  of  the  umbilical 
cord,  blood  no  longer  passes  through  the  umbilical  vessels, 
with  the  result  that  the  umbilical  vein  degenerates  into  a 
fibrous  cord  (round  ligament  of  the  liver).  The  hypogastric 
arteries  remain  pervious  for  the  first  part  of  their 'course,  as 
the  superior  vesicle  arteries ;  but  the  rest  of  their  course  is 
obliterated ;  they  degenerate  into  fibrous  cords. 

Development  of  vertebral  column:  Early  in  the  development 
of  an  embryo  there  is  formed,  beneath  the  medullary  groove, 
in  the  mesoblast  a  thin  thread  of  soft  cartilage  known  as 
the  chorda  dorsalis,  or  iwtorhorrf.  This  soon  becomes  in- 
cluded in  a  sort  of  fibrous  sheath,  and  is  the  primary  axis 


DEVELOPMENT  OF  THE  FACE.  297 

around  which  the  bodies  of  the  vertebrae  are  developed.  On 
either  side  of  the  notochord  are  developed  small  centres 
which  subsequently  split  (mesoblastic  somites).  These  are  the 
protovertebrce.  From  these  are  developed  the  vertebrae  and 
the  heads  of  the  ribs  by  the  inner  part;  and  by  the  outer 
(or  posterior)  part  the  muscles  and  skin  of  the  back,  the 
epidermis  being  derived  from  the  epiblast. 

The  vertebrae  are  not  formed  by  direct  ossification  of  the 
protovertebrse,  but  they  separate  in  such  a  way  that  adjacent 
protovertebrae  each  contributes  half  to  the  vertebra  formed. 
That  is,  two  protovertebrae  form  parts  of  two  vertebrae,  one 
above  and  the  other  below,  and  also  form  a  whole  vertebrae  by 
their  adjacent  portions. 

Development  of  cranium :  The  cranium  is  developed  from 
the  prolongation  of  the  tissues  over  the  protovertebrae  to  the 
cephalic  end  of  the  embryo.  Here  it  develops  three  seg- 
ments, corresponding  to  the  three  primary  vesicles  which  are 
the  forerunners  of  the  brain.  These  centres  of  ossification 
are  at  the  base  of  the  skull,  the  bones  of  the  vertex  being  de- 
veloped from  membrane. 

Development  of  the  face :  At  the  head  fold  of  the  embryo 
the  mesoblast  does  not  split  into  two  parts,  as  below,  but 
folds  in  from  the  side,  covered  without  and  within  by  the  epi- 
blast and  hypoblast.  These  folds  develop  certain  clefts  from 
which  the  face  is  derived,  the  mesoblast  furnishing  the  bone 
and  muscle  structures,  and  the  epiblast  the  epidermis,  while  the 
hypoblast  gives  the  mucous  membrane  which  lines  its  cavities. 

Immediately  below  the  anterior  cranial  vesicle  there  occurs 
on  either  side  a  cleft  in  the  lateral  fold  of  the  embryo  extend- 
ing to  the  vesicle  for  the  eye.  In  the  space  of  this  cleft  there 
is  developed  a  sort  of  secondary  cleavage  of  the  parts,  which 
by  the  rapid  growth  of  the  parts  included  between  the  clefts 
resembles  a  budding  (Fig.  151).  It  is  by  the  growth  of  these 
buds  or  processes  that  the  outline  of  the  face  is  formed.  From 
each  side  sprouts  the  superior  maxillary  process,  and  the  proc- 
esses unite  in  the  median  line,  and  with  the  nasal  or  inter- 
maxillary process  from  the  upper  border  of  the  cleft.  The 
portion  below  is  cut  off  by  a  branchial  cleft,  below  which  is 
the  mandibular  process  which  forms  the  lower  jaw. 


298  DEVELOPMENT. 

When  the  processes  do  not  unite  as  they  should,  various 
defects  occur  ;  most  common  are  those  about  the  mouth — viz., 
cleft  palate  and  hare-lip,  by  failure  of  the  superior  maxillary 
j n-ix v-.-es  to  unite  or  by  failure  of  the  intermaxillary  process 
to  unite  with  the  maxillary. 

The  other  branchial  clefts  do  not  persist  in  later  life.  They 
become  closed  as  they  accomplish  their  use  in  developing  cer- 
tain organs:  as  pathological  factors,  however,  we  are  often 
convinced  of  their  non-union  or  of  flaws  in  their  develop- 

FIG.  151. 


Development  during  first  month. 

ment,  cysts  and  tumors  of  various  kinds  and  certain  fistula 
being  attributable  to  this  cause. 

Development  of  the  extremities  :  They  develop  as  buds  from 
the  somatoblast  early  in  foetal  life,  and  the  formation  of  the 
joints  by  cleavage,  and  lesser  details  of  structure  are  gradu- 
ally worked  out.  At  about  the  third  month  the  separation 
of  the  fingers  and  division  of  the  extremity  into  joints  is 
about  completed.  The  arm  develops  somewhat  in  advance 
of  the  leg,  and  grows  rather  more  rapidly  in  the  earlier 
period  of  intra-uterine  life. 

Formation  of  the  spinal  cord:  It  will  be  remembered  that 
the  medullary  canal  encloses  in  its  cavity  cells  from  the  epi- 
blast  which  line  it.  These  cells  by  proliferation  and  differ- 
entiation develop  nerve-cells  and  nerve-fibres,  the  latter  at 
first  not  medullated.  The  cells  also  gradually  close  in  upon 
the  medullary  canal,  and  form  a  central  lined  with  epithe- 
lium, a  layer  of  nerve-cells  (gray  matter)  and  a  layer  of 
nerve-fibres  (white  matter). 


DEVELOPMENT  OF  THE  BRAIN.  299 

When  the  spinal  cord  first  appears  it  fills  the  entire  spinal 
canal,  but  at  the  time  of  birth  the  cord  has  apparently  not 
grown  so  rapidly  as  the  vertebral  column,  for  it  then  ends  at 
the  third  lumbar  vertebra,  and  in  the  adult  it  ends  at  the 
first.  Thus  we  are  able  to  explain  the  apparent  origin  of 
the  spinal  nerves  above  their  point  of  exit  from  the  canal, 
and  the  increasing  obliquity  of  the  nerves  from  above 
down,  until  finally,  in  the  tuft  of  vertical  nerves  below  the 
extremity  of  the  cord,  we  see  the  extreme  degree  of  this 
peculiarity. 

Development  of  the  spinal  nerves :  The  axis-cylinders  arise 
from  cells  of  the  epiblast  lining  the  medullary  groove. 
Before  the  closure  of  this  groove  to  form  the  medullary  canal 
an  offshoot  from  the  epiblast  may  be  observed,  which  is  the 
source  of  the  posterior  nerve-roots ;  and  they  become  attached 
to  the  cord  as  it  develops.  The  anterior  roots  spring  from 
the  cord  after  it  has  developed  fibres.  The  two  roots  then 
join  and  the  nerve  grows  out  into  the  mesoblast. 

Development  of  the  cranial  nerves :  In  much  the  same  way 
the  cranial  nerves  arise  primarily,  except  the  nerves  of  spe- 
cial sense.  In  function  the  motor  nerves  seem  to  form  a 
sort  of  anterior  root  for  the  sensory,  so  that  they  may  be 
arranged  in  pairs  corresponding  to  the  anterior  and  pos- 
terior roots  of  the  spinal  nerves ;  and  it  does  not  seem 
entirely  fanciful  to  regard  their  development  as  somewhat 
similar,  thus  : 

Third,  fourth,  sixth  and  seventh,  motor;  fifth,  sensory. 
Twelfth,  motor  ;  ninth,  sensory.  Eleventh,  motor  ;  tenth, 
sensory. 

Development  of  the  Brain. 

It  has  already  been  shown  how  from  the  growth  and  fusion 
of  the  two  sides  of  the  primitive  medullary  groove  a  tube 
is  formed ;  this  tube  representing  the  cerebro-spinal  axis. 
Starting  with  this  hollow  cylindrical  tube,  closed  at  both 
ends,  the  spinal  cord  and  brain  are  formed  as  a  result  of 
changes  in  the  size  of  the  lumen  of  the  tube,  alternate  thick- 
enings and  thinnings  of  the  walls  of  the  tube,  and  various 
foldings  and  reduplications  of  the  tube  on  itself. 


300 


DEVELOPMENT. 


Earliest  rudimentary  brain:  The  first  demarcation  between 
brain  and  spinal  cord  consists  of  a  widening  of  the  medullary 
canal  at  its  anterior  end.     At  the  same  time 
FIG.  152.  this  primitive  brain  is  subdivided  into  three 

portions  by  two  transverse  constrictions. 
The  three  chambers  are  known  as  the  an- 
terior primary  vesicle,  middle  primary  vesicle, 
and  posterior  primary  vesicle  (Fig.  152). 

Secondary  vesicles :  As  the  result  of  further 
development  the  posterior  primary  vesicle 
is  subdived  into  two  parts  by  a  transverse 
constriction.  The  anterior  primary  vesicle 
is  also  further  developed  by  a  forward 
growth  of  two  projections,  one  on  either 
side  of  the  median  line  (hemisphere  vesicles, 
Fig.  153). 

Ventricles  of  the  brain :  The  various  ven- 
tricles of  the  brain  are  the  successors  of  the 
original  lumen  of  the  cerebral  axis.  Thus 
we  see  that  the  lumen  of  the  prosencephalon 
is  known  in  the  developed  brain  as  the 
lateral  ventricles.  The  lumen  of  the  thala- 
mencephalon  is  the  third  ventricle,  and  the 
communication  between  the  two  lateral  ventricles  and  the 
third  ventricle  is  called  the  foramen  of  Monro.  The  lumen 
of  the  mesencephalon  (mid-brain)  becomes  the  aqueduct  of 
Sylvius.  The  cavity  of  the  epencephalon  (pons  and  cere- 
bellum) and  of  the  metencephalon  (medulla)  is  the  fourth 
ventricle. 

Development  of  the  walls  of  the  cerebral  tube  :  Commensu- 
rate with  the  division  of  the  primary  brain  into  its  vesicles, 
there  are  changes  going  on  in  the  walls  of  the  tube.  These 
changes  consist  of  thickenings  at  some  parts  and  thinnings  at 
others.  Thus  the  prosencephalon  shows  a  more  or  less  uni- 
form increase  in  thickness,  destined  to  become  the  substance 
of  the  cerebral  hemispheres,  corpora  striata,  etc. 

The  pons  Varolii  is  a  great  increase  ventrally  of  the  wall 
halon,  while  the  cerebellum  is  a  corresponding 
the  same  vesicle. 


Formation  of  the  ce- 
rebro-spinal  axis. 
1,  anterior  primary 
vesicle ;  2,  middle 
primary  vesicle ;  3, 
posterior  primary 
vesicle. 


3  R  A  R  V 


DEVELOPMENT  OF   WALLS  OF  CEREBRAL   TUBE.    301 
FIG.  153. 


Anterior  primary  vesicle. 


Middle  primary  vesicle. 


Posterior  primary  vesicle. 


Formation  of  secondary  vesicle, 
(diencephalon) 


1,  1,    prosencephalon ; 
mesencephalon ;  4,  epencephalon ;  5,  metencephalon. 


2,  thalamencephalon 


I.  Anterior 
primary 
vesicle. 


II.  Middle 
primary 
vesicle. 


III.  Posterior 
primary 
vesicle. 


(Cerebral  hemispheres, 
corpora   striata,  cor- 
pus callosum,  fornix, 
lateral  ventricles,  ol- 
(^    factory  bulb. 
2.  Thalamenceph-    f  Thalami  optici,  third 


1.  Prosencepha- 
lon. 


alon. 


\ 


3.  Mesencephalon.  <     ina 


4.  Epencephalon. 


5.  Metencephalon. 


ventricle,optic  nerve. 

Corpora  quadrigem- 
crura  cerebri, 
aqueduct  of  Sylvius. 

Cerebellum,  pons  Va- 
rolii,  anterior  part  of 
fourth  ventricle. 

Medulla  oblongata, 
posterior  part  of 
fourth  ventricle,  au- 
ditory nerve. 


302  DE  VELOPMEXT. 

The  preceding  table  enumerates  the  changes  described 
above. 

The  roof  of  the  fourth  ventricle,  in  its  lower  half,  is  de- 
scribed as  consisting  of  but  a  single  layer  of  epithelial  cells. 
This  is  a  result  of  a  thinning  of  the  dorsal  wall  of  the  meten- 
cephalon. 

Folding  of  the  brain-axis:  So  far  we  have  described  the 
brain  as  consisting  of  a  straight  tube  with  various  constric- 
tions and  changes  in  the  thickness  of  its  walls.  But  the  de- 
velopment is  not  so  simple  as  that.  The  brain  is  enclosed  in 
an  unyielding  box  (the  skull),  which  develops  and  grows  at 
the  same  time  that  the  brain  grows,  but  not  commensurately. 
The  brain  tends  to  grow  in  the  direction  of  its  long  axis,  but 
the  skull  grows  as  a  sphere;  hence  to  accommodate  itself  to 
the  containing  cavity,  the  brain  must  fold  on  itself — i.  e.,  coil 
up.  So  changes  take  place,  with  the  result  that  the  cercf>r<tt 
hemispheres,  instead  of  projecting  anteriorly,  grow  upward 
and  backward  so  as  to  overlie  the  third  ventricle.  There  is 
also  a  partial  turn  at  the  junction  of  the  mesencephalon  and 
epencephalon. 

Convolutions  of  cerebrum:  The  same  explanation  (different 
rates  of  growth  of  brain  and  skull)  serves  to  account  for  the 
presence  of  the  cerebral  convolutions.  The  surface  of  the 
cerebrum  is  "  puckered/'  as  it  were,  in  order  to  be  squeezed 
into  the  skull. 

Development  of  the  eye:  About  as  soon  as  the  cerebral 
vesicles  are  distinctly  formed  a  budding  of  two  projections- 
one  from  either  side  of  the  anterior  vesicle — occurs.  These 
are  the  primary  optic  vesicles.  They  are  formed  before  the 
vesicles  which  make  the  hemispheres  (prosencephalon).  The 
projections  approach  the  external  epiblast,  and  at  that  period 
consist  of  a  finger-like  process  having  a  globular  dilatation 
at  the  end.  This  subsequently  forms  the  optic  nerve  and  the 
retina. 

Opposite  the  optic  vesicle  the  superficial  epiblast  is  de- 
pressed and  forms  a  sort  of  pit,  forcing  the  optic  ve>icle  to 
fold  in  upon  itself.  The  follicle  of  epiblast  is  shut  off  at  the 
surface,  and  a  ball  of  its  substance  left  in  the  cup  of  the  in- 


DEVELOPMENT  OF  THE  ALIMENTARY  CANAL.      303 

folded  optic  vesicle.  This  ball  forms  the  rudimentary  lens, 
and  the  anterior  layer  of  the  vesicle  is  the  retina. 

The  muscular  and  vascular  structures,  as  well  as  the  con- 
nective tissue  and  humors,  are  derived  from  the  mesoblast, 
which  in  part  enfolds  the  ocular  vesicle  and  in  part  enters  it 
between  the  lens  and  the  edge  of  the  cup-like  depression. 
The  cornea  is  of  later  formation,  and  is  derived  from  the 
epiblast  of  the  skin. 

Development  of  the  auditory  apparatus :  Very  early  in  the 
life  of  an  embryo  there  is  a  depression  on  either  side  of  the 
head  which  passes  through  the  same  process  as  that  men- 
tioned for  the  crystalline  lens  and  for  the  germinal  epithelium 
in  the  formation  of  ova.  The  mass  of  epiblast  thus  separated 
forms  the  epithelium  of  the  labyrinth  and  vestibule,  the  sur- 
rounding mesoblast  furnishing  the  bony  and  muscular  struct- 
ures. The  auditory  nerve  is  developed  with  other  cranial 
nerves,  and  grows  in  to  its  end-organs  from  its  central 
origin. 

Development  of  the  olfactory  apparatus :  In  a  similar  way 
to  the  internal  ear  and  the  lens.  The  nasal  fossa  is  primarily 
a  depression  in  the  superficial  epiblast,  which  widens  and 
deepens  and  receives  the  nerve-filaments  from  the  olfactory 
lobe.  This  lobe  is  originally  a  bud  from  the  prosencephalon. 
The  primary  olfactory  depression  continues  to  widen  until  it 
opens  into  the  mouth,  and  is  again  shut  oif  by  the  growth  of 
the  "  branchial  arch/'  which  forms  the  superior  maxilla. 
The  nose  is  similarly  derived  from  the  mesial  and  lateral 
nasal  processes. 

Development  of  the  alimentary  canal :  As  has  already  been 
explained,  the  primitive  alimentary  canal  is  formed  from  the 
involution  of  the  splanchnopleure,  and  is  really  a  portion  of 
the  yelk-sac  partially  shut  oif  from  the  rest.  It  is  at  each 
end  a  blind  pouch  which  follows  the  head  and  tail  folds. 
The  portions  have  received  the  names  fore-gut  and  hind-gut 
as  they  occupy  one  or  other  of  these  folds. 

The  fore-gut  joins  with  the  mouth-cavity  by  the  folding 
back  of  the  epiblast  in  the  formation  of  the  stomadoeum,  and 
from  it  are  formed  the  pharynx,  oesophagus,  and  stomach. 

By  a  similar  involution  of  the  epiblast  the  anus  and  lower 


304  DEVELOPMENT. 

part  of  the  rectum  are  formed,  into  which  the  hind-gut  opens 
to  complete  the  alimentary  tract. 

The  oesophagus  is  sometimes  impervious  at  birth,  and  the 
rectum  or  anus  may  also  be  imperibrate.  This  is  caused  by 
the  non-union  of  the  segments  developed  from  the  epiblast 
with  those  developed  from  the  hypoblast. 

Glands  of  the  alimentary  tract :  (1)  The  salivary  glands  are 
developed  from  the  epiblast  lining  the  oral  cavity.  They  a  it- 
pear  primarily  as  a  simple  tube  which  develops  branches, 
about  which  the  alveoli  are  formed. 

(2)  The  pancreas  is  similarly  developed  from  the  hypoblast 
of  the  fore-gut. 

(3)  The  liver  is  primarily  a  protrusion,  into  a  mass  of  meso- 
blastic  tissue,  of  the  hypoblast  of  the  fore-gut,  which  appears 
as  soon  as  the  bloodvessels  begin  to  show  themselves.     The 
omphalo-mesenteric  vein,  from  the  umbilical  vesicle,  breaks 
up  into  a  capillary  plexus  in  this  same  tissue,  and  the  hepatic 
cells  develop  about  it. 

Derivation  of  the  lungs :  The  lungs  first  appear  as  a  bud  at 
the  junction  of  pharynx  and  oesophagus  which  soon  forms  a 
separate  tube  (the  trachea).  The  cells  from  the  hypoblast  ex- 
tend into  the  surrounding  mesoblast,  and  it  is  from  this 
structure  that  all  of  the  tissues  of  the  lungs,  except  its  epithe- 
lium, are  formed. 

The  Wolffian  body  is  first  seen  as  early  as  the  third  week  as 
a  series  of  transverse  tubes  which  develop  in  the  cells  of  the 
mesoblast,  just  inside  of  its  division  into  parietal  and  visceral 
layers,  on  each  side  of  the  vertebral  column.  It  is  not  a 
permanent  organ.  Internal  to  it  develop  the  internal  organs 
of  generation,  while  behind  the  Wolffian  body  the  rudimen- 
tary kidney  develops. 

The  Wolffian  body  is  a  sort  of  temporary  kidney.  At  first 
it  is  a  large  vascular  body,  resembling  the  kidney  in  structure, 
and  opens  by  its  tubes  (outer  ends,  the  inner  ends  being  blind) 
into  the  Wolffian  duct,  which  leads  to  and  opens  into  the 
cloaca.  At  about  the  sixth  week  of  foetal  life  the  kidney 
begins  to  grow  and  the  temporary  organ  to  atrophy.  As  this 
occurs  a  duct  for  the  kidney  (the  ureter)  is  developed  from 
the  Wolffian  duct.  The  use  of  the  organ  seems  to  be  that  of 


PARTURITION.  305 

a  temporary  kidney ;  but  by  the  end  of  the  third  month  it 
has  been  replaced  by  the  permanent  organ,  and  has  almost 
entirely  disappeared. 

Formation  of  the  internal  genitals  :  The  body  (germinal 
epithelium)  which  appears  on  the  inner  side  of  the  Wolman 
body  is  the  nucleus  of  the  future  testicle  or  ovary,  while  along 
the  outer  side  are  formed  two  ducts  (Miiller's  and  the  Wolf- 
fian),  which  pass  down  to  the  cloaca  or  lower  end  of  the 
hind-gut.  At  first  it  is  impossible  to  determine  the  sex  of  the 
foetus. 

If  the  foetus  is  to  become  a  female,  the  ducts  of  Muller 
join  to  form  the  uterus  and  vagina,  while  the  ununited  por- 
tions remain  as  the  Fallopian  tubes.  The  Wolffian  ducts  are 
rudimentary  in  the  female  and  appear  as  the  ducts  of  Gart- 
ner. 

On  the  other  hand,  if  the  male  type  is  to  be  formed,  the 
Wolffian  ducts  become  convoluted  tubules,  and  each  is  at- 
tached to  the  testis  as  the  epididymis  and  vas  deferens. 
Miiller's  duct  is  rudimentary  in  the  male,  and  is  only  found 
as  the  sinus  pocularis  and  the  hydatids  of  Morgagni. 

Formation  of  external  genitals  :  In  both  sexes  in  early  foetal 
life  the  external  genitals  are  alike,  consisting  of  a  body  re- 
sembling a  penis  with  a  fold  of  skin  at  either  side.  In  the 
female  this  body  becomes  proportionally  smaller,  and  appears 
as  the  clitoris,  the  two  lateral  masses  becoming  the  labia  ma- 
jora.  In  the  male  a  groove  on  the  under  surface  unites  at  its 
borders  to  form  the  urethra,  while  the  scrotum  is  formed  from 
the  folds  of  skin  at  the  side.  This  differentiated  condition 
may  persist  in  adult  life,  and  has  been  mistaken  for  hermaph- 
rodism. 

PARTURITION. 

By  parturition  is  meant  the  expulsion  of  the  foetus  at  a 
viable  age  from  the  mother.  The  average  time  for  the  full 
development  of  the  foetus  is  given  at  two  hundred  and  sev- 
enty-eight days.  During  this  time  (period  of  gestation)  the 
foetus  depends  absolutely  for  its  existence  upon  the  mother. 
After  parturition  the  child  aerates  its  blood,  ingests  food,  and 
purifies  its  body  of  wastes  for  itself,^ 

20-Ph.ys. 


306  PARTURITION. 

Method  of  expulsion  of  foetus  :  The  foetus  is  expelled  in 
part  by  the  contraction  of  the  uterine  muscles,  and  in  part  by 
the  pressure  exerted  by  the  abdominal  walls.  The  uteri  IK? 
contractions  are  the  first  to  appear,  and  it  is  not  until  the 
foetus  enters  the  vagina  that  the  abdominal  muscles  are  brought 
into  play. 

Causes  of  uterine  contractions  :  As  to  this  no  satisfactory 
answer  has  been  given.  Why  the  uterus  should  contain  the 
growing  embryo  for  months,  and  then  be  suddenly  thrown  into 
action  to  expel  it,  cannot  be  explained. 

Nature  of  parturition :  It  is  a  reflex  action  depending  upon 
a  centre  in  the  lumbar  spinal  cord.  Whence  the  stimuli  are 
derived  which  excite  the  reflex  is  unknown,  but  probably 
from  the  organ  itself. 

Character  of  uterine  contractions :  They  are  rhythmical  in 
character,  and  may  be  compared  to  the  contractions  of  the 
heart-muscle.  Each  "pain"  begins  feebly,  gradually  in- 
tensifies until  it  reaches  a  maximum,  and  then  gradually  de- 
clines until  it  entirely  dies  away,  to  be  succeeded  by  another 
similar  contraction  and  pause.  This  rhythmical  action  con- 
tinues until  the  uterine  contents  are  expelled,  and  then  the 
organ  enters  into  a  condition  of  tonic  contraction. 

After  parturition,  by  a  process  of  involution  lasting  for  a 
few  weeks,  the  uterus  returns  to  its  normal  unimpregnated 
state. 


APPENDIX. 


TABLE  OF  THE  DEVELOPMENT  OF  AN  EMBRYO. 

(Modified  from  Gray's  Anatomy.) 

1st  Week. — Ovum  in  Fallopian  tube.     Segmentation  of  vitellus. 

2d  Week. — Ovum  in  uterine  decidua.  Chorion.  Formation  of 
blastoderm  and  division  of  mesoderm.  Heart  and  medullary  groove. 
Amnion  and  umbilical  vesicle  formed.  Allantois. 

3d  Week. — Head  and  tail  flexures.  Closure  of  medullary  canal,  and 
formation  of  primary  cerebral  vesicles  and  ocular  and  auditory  vesi- 
cles. Branchial  arches.  Wolffian  bodies.  Limbs. 

4th  Week. — Limbs  increased.  Anal  opening.  Interventricular  sep- 
tum begins.  Ant.  spinal  nerve-roots.  Olfactory  fossae.  Lungs.  Pleurae. 

5th  Week. — Allantois  vascular.  Trace  of  feet  and  hands.  Miiller's 
duct  and  genital  gland. 

6th  Week. — Umbilical  vesicle  disused.  Branchial  clefts  close.  Post- 
spinal  nerve-roots.  Membranes  of  the  nervous  centres.  Bladder. 
Kidneys.  Tongue.  Larynx. 

7th  Week. — Muscles  perceptible.    Many  centres  of  ossification  appear. 

8th  Week. — Joints  appear  in  extremities;  fingers  and  toes  separate. 
Crystalline  lens.  Salivary  glands.  Spleen.  Interventricular  septum 
complete.  Sympathetic  nerves. 

9th  Week. — Distinction  between  ovary  and  testicle.  Genital  furrow. 
Pericardium. 

3d  Month.— Formation  of  placenta.  External  genitals  separate  from 
anus.  Eyelids,  hairs,  and  nails.  Duct  of  Wolffian  body  joins  testicle. 

Jf,th  Month. — Middle- ear  bones.  Tympanum  and  labyrinth.  Scrotum 
and  prepuce. 

5th  Month. — Germs  of  teeth.  Hair-  and  sweat-glands.  Brunner's 
glands.  Uterus  and  vagina  distinctly  separate. 

6th  Month. — Papillae  of  skin.  Sebaceous  glands.  Peyer's  patches. 
Free  border  of  nails. 

7th  Month. — Cerebral  convolutions.  Pupillary  membrane  disappears. 

8th  Month. — Descent  of  testis. 

9th  Month. — Opening  of  eyelids.     Ossification  of  cochlea. 

CHEMICAL  TESTS  USED  COMMONLY  IN  PHYSIOLOGI- 
CAL ANALYSIS. 

FOR  PROTEIDS  : 

Nitric  Acid  coagulates  all  except  peptones. 

Heat. — All  are  coagulated  by  boiling,  except  peptones. 

307 


308  APPENDIX. 

XanthojH'Oteic  Reaction. — A  solution  boiled  with  strong  nitric  acid 
becomes  yellow  :  the  color  is  deepened  by  the  addition  of  ammonia. 

Biuret  RatHinn. — With  a  trace  of  copper  sulphate  and  an  excess  of 
potassium  or  sodium  hydrate  they  give  a  purple  reaction. 

Millon's  Reaction. — With  a  solution  of  metallic  mercury  in  strong 
nitric  acid  (Millon's  reagent)  they  give  a  white  or  pinkish  rear  lion, 
and  the  color  becomes  more  pink  on  boiling. 

FOR  STARCH: 

Iodine  Reaction. — Add  to  a  solution  of  starch  a  small  quantity  of 
tincture  of  iodine,  and  a  blue  reaction  results.  The  color  disappears 
on  heating  and  returns  on  cooling. 

Glycoyen. — Same  test  gives  reddish  reaction,  port-wine  color,  which 
disappears  on  heating  and  returns  on  cooling. 

FOR  SUGAR  (GLUCOSE)  : 

Moore's  Test. — Boil  solution  of  sugar  with  an  excess  of  potassium 
hydrate,  brown  color-reaction. 

Trommer's  Test. — Add  to  solution  a  sufficient  amount  of  potassium 
hydrate  to  render  it  quite  strongly  alkaline.  Then  add  a  solution  of 
copper  sulphate,  drop  by  drop,  until  a  distinct  blue  tinge  is  visible. 
Heat,  and  the  presence  of  sugar  is  shown  by  the  appearance  of  red, 
yellow,  or  orange  color-reaction. 

Fehling's  Test  Solution. — An  alkaline  copper  solution  by  which  a 
quantitative  test  may  be  made.  The  solution  is  somewhat  unstable, 
and  is  for  this  reason  to  be  tested  by  boiling  before  using.  The  strength 
of  the  solution  is  such  that  1  cubic  cm.  (15  minims)  will  be  exactly 
decolorized  by  ^yth  of  a  gramme  (.075  grain)  of  glucose.  This  test 
is  very  delicate,  and  is  quite  commonly  used  for  urinary  examinations 
to  detect  glycosuria. 

The  Fermentation  Text. — If  a  small  quantity  of  yeast  be  added  to  a 
sugar  solution,  the  fungus  of  the  yeast  (saccharomyces)  will  cause  the 
sugar  to  be  decomposed  into  carbonic  acid  and  alcohol.  If  the  process 
be  continued  until  the  sugar  is  entirely  broken  up,  the  amount  of  car- 
bonic acid  evolved  indicates  the  proportion  of  sugar  present. 

FOR  BILE-SALTS  : 

Pettenkofer's  Test. — Upon  the  addition  of  sulphuric  acid  to  a  solution 
of  bile-salts  in  water  there  is  a  precipitation  of  the  salts,  which  are 
redissolved  by  a  further  addition  of  the  acid.  If  a  drop  of  a  solution 
of  cane-sugar  be  added,  a  deep  cherry  color  is  developed. 

FOR  BILE-PIGMENTS  : 

Gmeliii's  Test. — Add  a  small  quantity  of  nitroso-nitric  acid  to  a  solu- 
tion of  the  bile-piirments,  and  a  play  of  colors  result,  l>eirmnin<:  with 
green  and  changing  to  blue,  violet,  red,  and  yellow.  This  is  seen  best 
on  a  white  background ;  therefore  a  plate  is  often  used  for  this  test. 


APPENDIX.  309 

METRIC    SYSTEM. 


1  Inch  12  '  3 


1 1 1 1 1 1  1  1 2  i  3  ,4  15  |6  |7  18  |910 

Millimetres.  Centimetres. 


Square  i 

Centi-   ; 


The  area  of  the  figure  within  the  heavy  lines  is 
that  of  a  square  decimetre.  A  cube  one  of  whose 
sides  is  this  area  is  a  cubic  decimetre  or  litre.  A 
litre  of  water  at  the  temperature  of  4°  C.  weighs  a 
kilogramme. 

A  litre  is  1.76  pint;  a  pint  is  0.568  of  a  litre. 

The  smaller  figures  in  dotted  lines  represent  the 
areas  of  a  square  centimetre  and  of  a  squre  inch. 

A  cubic  centimetre  of  water  at  4°  C.  weighs  a 
gramme. 


Square  Inch. 


Metre  =  39f  inches. 
Centimetre  =  f  inch. 
Millimetre  =  ^  inch. 
Micromillimetre  =  ^tjnu  inch. 

Gramme  =  15^  grains. 
Centigramme  =  ^  grain. 
Milligramme  =  ^ifo  grain. 
Kilogramme  =  2.2  pounds. 


INDEX. 


A. 

Absorption,  111-115 

carbohydrates,  113 

destination  of  food,  113 

fats,  113 

favoring  factors,  111 

from  stomach,  101 

intestinal,  102 

peptones,  113 

salts,  113 

sites,  111 

sugars,  113 

water,  113 

Accommodation,  250 
Achromatism,  259 
Acid,  hippuric,  135 

hydrochloric,  97,  98 

uric,  135 
After-images,  259 

negative,  260 

positive,  260 
Air,  82-84 

complementary,  83 

expired,  83 
composition,  33 
weight,  83 

inspired,  83 
composition,  83 

reserve,  82 

residual,  83 

tidal,  82 

vitiated,  88 
Albumin,  serum,  114 
Allantois,  289 

history,  289 

purpose  of,  289 
Am n ion,  288 

fluid,  289 

purpose  of,  288 
Amoeba,  22 

functions,  22,  23 
Amylopsin,  105 
Anabolism,  18 


Anaesthesia,  201 
Animal  heat,  140-142 
loss  of,  141 
regulation  of,  141 

centres,  142 
sources  of,  140 

chemical  action,  140 
friction,  141 

oxidation  of  tissues,  140 
warm  media,  141 
Aphasia,  201 
Apncea,  87 
Apparatus,  23 
Aqtieductus  vestibuli,  237 
Aqueous  humor,  247 
Area  germinativa,  284 

vasculosa,  293 
Arterial    contraction    and    dilatation 

(see  also  Arteries),  66 
tension  (see  also  Arteries),  59 
Arteries,  54 
action,  67 
contraction,  66 
dilatation,  66 
elasticity,  58 
nerve-supply,  67 
vaso-constricior,  67 
vaso-dilator,  67 
resiliency,  56 
size,  55 
structure,  54 
tension,  59 

conditions  modifying,  59 
tone,  67 

vasa  vasorum,  54 
vaso-motor  nerves,  54 
Asphyxia,  87 
Assimilation,  140 
Astigmatism,  262 

Atmosphere,  vitiated  'see  also  Air),  88 
Auditory  apparatus,  232 
canal," 233,  238 
external,  233 
internal,  238 

311 


312 


INDEX. 


Auditory  nerve,  238 
Auricle,  233 

Auricles  of  heart,  51 

action,  ">1 

regurcitation  hindered,  52 
Axis-cylinder,  159,  160,  161 
Axons^  163 

B. 

Bacterium  lactis,  121 
Bile,  106 
amount,  107 
character,  107 
composition,  107 
pigments,  108 

(imelin's  test,  108 
tests  for,  310 
salts,  107 

Pettenkofer's  test,  108 
test  for,  310 
use  of,  in  digestion,  109 
Bilirubin,  108 
Biliverdin,  108 
Bladder,  129 
Blastoderm,  284 
Blastoderm ic  membrane,  283 
Blind-spot,  252 
Blood,  30-46 
arterial,  31 
circulation  (see  also    Circulation  of 

blood),  48-70 
frog's  foot,  59 
coagulation  (see  also  Coagulation  of 

blood),  42 
coagulum,  44 
buffy-coat,  44 
corpuscles  (see  also  Corpuscles  of 

blood),  32-40 
plates,  32-40 
red,  32-38 
white,  32-38 
foatal,  290,  291 
function  of,  46 
uases,  42 

-i IKS  appearance,  30 
lack  of  oxygen,  87 
liquor  sanguinis,  32 
maternal.  290,  291 
opacity,  31 

physical  characteristics,  31 
-plasma,  :;•_',  40 
clotting,  41,  42 
properties,  41 

-plates,  40 

-pivs<mv    (>ee    also    Circulation  of 
\  57 


Blood,  quantity,  32 

reaction,  31 

-serum,  41 

specific  gravity,  31 

taste,  31 

venous,  31 
Body,  analysis,  24 

energy  of,  138 

expenditures,  138 

results  of,  138 

temperature  of,  140 

limits,  142 
Brain  (see  also  Cerebrum),  192  •.'<)! 

development,  300-303 

fibres,  197 
association,  197 
commissural,  197 
medullary,  197 

relation  of  size  to  intellect,  197 

ventricles  of,  301 

weight,  197 

Branchial  cleft,  298,  299 
Bronchi,  77 

c. 

Canal  is  cochlearis,  237 

reunions,  237 
Capillaries,  54 
Carbohydrates,  29,  30,  113 
Cells,  18-24 

blood  (see  also  Blood),  23 

connective  tissue,  24 

decay,  21 

development,  21 

endothelium,  24 

epithelium,  23 
varieties,  23,  24 

gemmation,  20 

karyokinesis,  20 

nerve,  (see  also  Nervous  system',  23 

nucleolus,  19 

nucleus,  19 

protoplasm,  19-22 
difference    between     plants    and 
animals,  23 

specialization,  23 

structure,  18 
Centimetre,  311 
Centres  (see    ^/limil  cord,  M«lull<i  ub- 

lo-ngata,  and  Cerebrum). 
Cerebellum,  201-203 

function.  203 

gray  matter,  201,  202 

peduncles,  201 

removal  of,  205 
Cerebro-spinal  system,  169,  174-220 


INDEX. 


313 


Cerebrum,  192-201 

chemistry  of  brain-tissue,  196 
convolutions,  193 
cortex,  196 
functions,  198 

localization  of,  199,  200 
centres  of  special  senses,  199 
motor  areas,  199 
sensory  areas,  199 
gray  matter,  195 
lesions,  204 
lobes,  193,  194 
mutilations,  204,  206 
regions,  193 
surface,  193 
unilateral  action,  199 
Chlorophyl,  27 
Cholesterine,  109 
Chorda     tympani    (see     also    Cranial 

nerves),  213 
Chorion,  289 

association  with  decidua,  290 
villi,  289 
Choroid,  246,  259 
pigment  of,  259 
Chyle,  47 
Chyme,  100,  111 
Ciliary  muscle,  247 
Circulation  of  the  blood,  48-70 
apparatus,  48 

arteries  (see  also  Arteries),  48 
capillaries  (see  also  Capillaries),  49 
heart  (see  also  Heart),  48 
veins  (see  also  Veins),  49 
blood-pressure,  57 
in  arteries,  58 
continuous,  58 
intermittent,  58 
small,  58 
in  capillaries,  58 
manometers,  57 
in  veins,  58 
course,  49 
aorta.  49 
arteries,  49 
capillaries,  49 
left  auricle,  49 
left  ventricle,  49 
pulmonary  arteries,  50 

veins,  49 
right  auricle,  49 
veins,  49 
foetal,  252 

change  from,  to  adult,  295 
course,  294 
effects  of,  294 


I  Circulation,  forces,  56 

arterial  resiliency,  56 
contraction  of  muscles,  56 

of  veins,  57 
heart,  56 
suction,  cardiac,  56 

thoracic,  56,  69 
placenta,  292 

characteristics,  294 
portal,  50 
pulmonary,  50 
speed,  57 

in  arteries,  57 
in  capillaries,  57 
in  veins,  57 

ratio  between,  and  pressure,  57 
systemic,  50 
vitelline,  292 
Climacteric,  275 
Coagulation  of  blood,  42-45 
conditions  affecting,  43 
hastening,  43 
air,  43 

foreign  bodies,  43 
rest,  43 
warmth,  43 
water,  43 
retarding,  43 
acids,  43 
agitation,  43 
alkalies,  43 
cold,  43 
ferments,  43 
heat,  43 

living  tissues,  43 
no  air,  43 
salts,  43 

viscid  substances,  43 
water,  43 
corpuscles,  43 
explanation,  44 
fibrin,  43 
plasma,  43 
serum,  43 

Cochlea,  235,  236-238 
Coitus,  281 
Collaterals,  175 
Color-blindness,  262 
causes,  264 

in  different  sexes,  264 
importance  of,  265 
test  for,  265 

Color-perception,  259,  262 
normal,  262 

theories  of,  262,  263 
Colostrum,  120 


314 


INDEX. 


Colostrum  corpuscles,  120 
Commissure  of  Gudden,  255 
Cones,  251 

Connective  tissue,  24 
Contractions,  uterine  (see  also  Uterus, 

(•'infractions  of),  307 
Coordination,  184 
Copulation,  269 
Cornea,  245,  246 
Corpora  quadrigemina,  191,  192 

striata,  196,  198 
Corpus  callosum,  192 
lut i-ii in.  277 
of  menstruation,  277 
of  pregnancy,  277 
Corpuscles  of  blood,  32-40,  59 
Pacinian,  164 
plates,  32,  40 
red,  32-38 
color,  33 
diapedesis,  37 
function,  35 
globulin,  35,  36 
hsematin,  35,  36 
hsemin,  35,  36 
haemoglobin,  35,  37 
oxy-,  37 
reduced,  37 
spectra,  37,  38 
number,  32 
origin,  34 

physical  characteristics,  32,  33 
specific  gravity,  33 
of  vertebrates,  33 
touch,  164 

white  (see  also  Leukocytes),  38-40 
Corti,  organ  of,  238 

rods  of,  238 
Cranial  nerves,  206-220 

I.  nerve  (see  also  Nerve,   olfactory), 

230 

II.  nerve  (see  also  Nerve,  optic),  253 

III.  nerve,  207 
function,  207 
origin,  207 

IV.  nerve,  208 
function,  208 
origin,  208 

portio  dura,  2]  2 
portio  moll  is,  212 
trochlear,  208 

V.  nerve,  208 
origin,  208 
route,  208 

motor,  208 
sensory,  208,  209 


Cranial  nerves, V.  nerve,  sensory  route, 

trophic  influence,  211 
influence  on  special  senses,  211 

VI.  nerve,  211 

VII.  nerve,  212 
chorda  tyrupani,  213 

eflect  on  taste,  214 

secretion,  213 
distribution,  213 
function,  213 
origin,  212 
paralysis  of,  213 

VIII.  nerve   (see  also  Nerve,   audi- 
tory), 238 

IX.  nerve,  215 
function,  215 

deglutition,  215 
taste,  215 
origin,  215 

X.  nerve,  216 
communication  with  other  nerves, 

216 

in  deglutition,  218 
distribution,  216 
function,  217,  218,  219 
influence  on  heart,  218 
origin,  216 

relation  to  stomach,  218 
in  respiration,  86,  87,  217 

XI.  nerve,  219 
functions,  219 

holding  breath,  219 
voice,  219 
origin,  219 

XII.  nerve,  220 
functions,  220 

indigestion,  220 

speech,  220 
origin,  220 
Cream,  120 
Cristse  acusticse,  236 
Crura  cerebri,  191,  192 
Crystalline  lens,  247 
Cumulus  proligerus,  271 

D. 

Decidua  nienstrualis,  276,  284 

reflexa,  284 

vera,  284 
Decimetre,  cubic,  311 

square,  311 
Defecation,  110 

centre,  183 
Defective  eyes,  260 
Definition  of  physiology,  17 


INDEX. 


315 


Deglutition,  94 
actions  of,  94 
nerves  in,  94 
Deiidrites,  162 
Development,  283-307 
alimentary  canal,  304 
auditory  apparatus,  304 
of  brain,  300-303 
of  circulatory  apparatus,  293 
of  cranial  nerves,  300 
of  cranium,  298 
of  extremities,  299 
of  eye,  303 
of  face,  298 
of  genitals,  306 

internal,  306 

external,  306 
of  heart,  293 
of  kidney,  305 
of  liver,  305 
of  lungs,  305 

of  olfactory  apparatus,  304 
of  ovary,  306 
of  pancreas,  305 
of  salivary  glands,  305 
of  spinal  cord,  299 
of  spinal  nerves,  300 
of  testicle,  306 
of  ureter,  305 
of  uterus,  306 
vagina,  306 

of  vertebral  column,  297 
Dextrose,  114 
Dialysis,  111 

Diastole  (see  also  Heart),  61 
blood-supply,  63 
force,  63 
inner vation,  65 

accelerator,  66 

depressor,  66 

ganglia,  65 

inhibitory,  65 

sympathetic,  66 

vagus,  65 
sounds,  62 

first,  63 

second,  63 
systole 

auricular,  61 

ventricular,  61 
Diet,  138,  139 
"exclusive,"  138 
normal,  139 
over-feeding,  139 
Digestion,  90-108,  111 
gastric  (see  also  Gastric  digestion),  100 


Digestion,  intestinal,  101 

large  intestine,  110 

pancreatic,  106 

products  of,  113 
Diplopia,  262 
Discus  proligerus,  271 
Distance,  240 
Drink,  137 
Duct, 

Gartner's,  305 

Miiller's,  305 

Wolflian,  306 
Due  bus  arteriosus,  295 

endolyniphaticus,  237 

venosus,  294 
Dyspnoea,  87 

E. 

Ear,  232 

external,  232,  233 

internal,  232,  235 

middle,  232,  233 
Elimination,  channels  of,  18 
Embryo,  development  of,  309 
Embryology,  267-307 
Emulsification,  105 
Encephalon,  301,  302 

ep-,  302 

nies,  302 

met-,  302 

pros-,  302 

thalam-,  302 
Eudolymph,  235,  239 
Endothelium,  24 
End-plates,  163. 
Epiblast,  285 

structures  derived  from,  286 
Epididymis,  279 
Epithelium,  23,  24 

germinal,  271 

varieties,  23,  24 
Equilibrium,  236 
Eustachian  tube,  233,  235 

valve,  295 
Excretion,  115,  137 

process  of,  115 

Expiration  (see  also  Respiration),  81 
Eye,  243,  245 

accessory  regions,  243 
Eyeball,  245 

coats  of,  245 
choroid,  246 
cornea,  245,  246 
retina,  246 
sclerotic,  246 

development,  303 


316 


INDEX. 


Eyeball,  eminetropic,  260 
function,  243 
lids,  244 
muscles  of,  244 

F. 

Facial  neuralgia,  211 

paralysis,  213 
Fallopian  tubes,  273 

function,  273 
Fats,  29,  30,  113 
Fecundation,  2<>9,  281 
Fenestra  oval  is,  233 

rotunda,  233 

Ferments,  pancreatic,  105 
Fertilization,  methods,  281 
Fibrin,  44 

ferment,  44 
Fibrinogen,  40,  41,  44 
Foatal  circulation  (see  also  Circulation, 

festal),  292 

Foetus,  expulsion,  307 
Folds,  285,  298 
Food,  137 
Food-stuffs,  30 

carbohydrates,  29,  30 

fats,  29,  30 

proteids,  28,  30 
Foramen  ovale,  295 
Fovea  centralis,  252 
Funiculus  cuneatus,  187 

gracilis,  187 

G. 

Gall  (see  also  Bile),  106 
-bladder,  106 
-ducts,  106 

Ganglia  of  sympathetic  (see  also  Sym- 
pathetic system},  171,  172 
Ganglion,  171 
cervical,  172 
cceliac,  172 
impar,  172 
ophthalmic,  171 
otic,  171 
semi  lunar,  172 
spheno-palatine,  171 
submaxillary,  171 
thoracic,  172 
(iasrs  in  blood,  42 

carbon  dioxide,  42 
nitrogen,  42 
oxygen,  42 
Gastric  digestion,  100 

conditions  favoring,  100 


Gastric  digestion,  nervous  mechanism, 

100 

time  required,  100 
juice,  97 

composition,  97 
functions,  98 
secretions,  98 
Gelatins,  28 
Gemmation,  20 
Generation,  asexual,  268 
organs  of,  269,  278 
female,  269-278 
male,  278-280 
Geniculate  bodies,  255 
Germ-hill.  271 

Germinal  epithelium,  271,  300 
membrane,  283 
spot,  273 
vesicle,  273 
Gestation,  306 
Glands,  ductless.  135 

purpose  of,  136 
of  intestine  (see  also  Intestine),  102- 

104 

lachrymal,  244 
mammary  (see  also  Mammary  glands), 

119 

Meibomian,  244 
prostate,  280 
sebaceous,  122 
sweat,  122 
vascular,  135 
Glandular  activity,  117 

conditions  affecting,  117 
amount  of  blood,  117 

of  material,  117 
nervous  system,  117 
Glosso-labio-laryngeal  paralysis,  191 
Glottis,  241 
Glycogen.  110,  114 

in  muscle,  145 
Graafian  follicle,  270 

maturation  of,  271 
Gramme,  311 
Gustatory-buds,  227 
Gut,  fore',  304 
hind,  304 

H. 

Hair,  124 

-follicle,  124 
Hallucinations,  221 
11.  a  ring,  232-241 

c.-ntre,  199 

localization,  199,  240 

musical  range  of,  ~ 1 1 


INDEX. 


317 


Hearing,  subjective,  240 
Heart,  51-54,  61 

action,  61 

apparent  elongation,  61 

auricles,  51 

beat,  61 
diastole,  61 
systole,  61 

cardiac  cycle,  62 

development  of,  293 

rate,  61 

situation,  51 

size,  51 

ventricles,  51 

weight,  51 
Heat,   animal  (see  also  Animal 

140-142 
Hemiansesthesia,  201 
Hemiplegia,  201 
Hemispheres  of  cerebellum,  201 

of  cerebrum,  192 
Heredity,  267 
Hippuric  acid,  135 
Hymen,  274 
Hypermetropia,  261 
Hyperpnoea,  87 
Hypoblast,  285 

structures  derived  from,  287 

I. 

Impregnation,  281 
details,  282 
site  of,  282,  283 
time  of,  282 
Incus,  234 
Inhibition,  185-189 
Insalivation,  92 
Inspiration  (see  also  Respiration), 

81 

Intestine,  juice,  104 
large,  110 

absorption,  110 
digestion,  110 
structure,  110 
peristaltic  action,  102-111 
small,  101-104 
glands,  102-104 
agminate,  104 
Bru  nner's,  103 
Lieberkiihn's,  103 
Peyer's,  103 
solitary,  103 
Iris,  248,  259 


78- 


Judgments,  222 


J. 


K. 

Caryokinesis,  20 
Catabolism,  18 
Kidneys,  126-135 
blood-supply,  128 
arteries,  129 
afferent,  129 
arterise  rectse,  129 
iuterlobular,  129 
veins,  129 
efferent,  129 
interlobular,  129 
venae  rectse,  129 
cortical  portion,  127 
medullary  portion,  127 
size,  126 
weight,  127 

L. 

Labyrinth,  bony,  235 

membranous,  235 
Lacteals,  70-113 
^actose,  121 
Lamina  spiral  is,  236 
Larynx,  76,  241 

lesions  in  brain  and  cord,  203,  204 
Leukocytes,  38-40 ;  46,  59 
characteristics,  38 
chemical  composition,  39 
death,  40 
function,  40 
emigration,  38,  60 
phagocytosis,  40 
number,  32 
occurrence,  38 
origin,  39 
varieties,  39 
lymphocytes,  39 
mononuclear,  39 
polynuclear,  39 
Life,  17 

living  body  compared  to  machine,  17 
Litre,  311 
Liver,  106-110 
functions,  106 

elaboration  of  urea,  106,  110 
excretion,  106,  109 
glycogenic,  106,  109 
secretion,  106 
Lochia,  292 
Lungs,  77 

capacity  of,  82 
minute  anatomy,  77 
Lymph,  46-48 


318 


INDEX. 


Lymph  coagulation,  47 
chyle,  47 
circulation,  70 
composition,  46 
flow,  70 

factors  in,  73 
ganglia,  73 
pressure,  72 

Lymph  spaces,  46,  70,  113 
sources,  47,  72 

intercellular  spaces,  47 
lacteals,  47 
uses,  47 
Lymphatic  nodes,  73 

purpose,  74 
Lymphatics,  70 
structure,  72 
Lymphocytes,  39 

M. 

Macula  acustica,  236 

lutea,  252 
Malleus,  234 
Malpighian  bodies,  127 
Mammary  glands,  119 
secretion,  119 
structure,  119 
alveoli,  119 
lobes,  119 
lobules,  119 
Mastication,  90 

muscles,  92 
Mastoid  cells,  233 
Medulla  oblongata,  185-191 
automatic  action,  189 
centres,  189 
conduction,  188 
function,  188-190 
gray  matter,  187 
gross  anatomy,  185 
inhibition,  189 
reflex  action,  188 
Medullary  canal,  299 
groove,  285 
sheath,  159,  160 
Membrana  basilaris,  237 

tympani,  234 

Membrane,  blastodermic,  283 
germinal,  283 
of  Reissner,  237 
vitelline,  272 
Menopause,  275 
Menstruation,  274 
connection  with  ovulation,  278 
corpus  luteum  of,  278 


Menstruation,  definition,  274 
discharge,  276 
duration,  275 
frequency  of,  275 
nature,  275 
Mesoblast,  285 
changes  in,  286 
structures  derived  from,  286 
Metabolism,  18 
Metric  system,  311 
Microcytes,  40 
Micturition,  133 
Milk,  119 

composition,  119 
secretion,  120 
Mouth,  90 
Mucin,  118 
Mucus,  118 
Muller's  duct,  306 
Muscle,  142-159 
chemistry  of,  144 
conductivity,  155 
contractility,  148,  149 
contraction,  148 
artificial  stimuli,  150 
chemical,  150 

electrical,  150,  151,  152,  153 
mechanical,  150 
response  to,  151 
thermal,  150 
path  of  stimulus,  148 
Pfliiger's  law.  !."> 
results  of,  157 
currents,  ascending,  156 
descending,  156 
of  rest,  1  •">  1 
electrical  state,  154 
excitability,  155 
fatigue,  147 
general  properties,  144 
latent  period,  147,  152 
apparent,  147 
true,  147 
as  levers,  146 
nerve-muscle  preparation.  157 

conditions   influencing    results, 

157 

order  of  fatigue,  157 
oxygen-supply,  1 1<> 
physiology  of,  145 
activity,  145 
rest,  145 
rigor,  145 
plasma,  144 
varieties,  142 
non-striated,  142 


INDEX. 


319 


Muscle,  varieties,  striated,  142 
involuntary,  142,  144 
voluntary,  142,  143 
Mutilations,  204,  205 

brain,  204 

cerebellum,  204 

cord,  204 
Myopia,  260 
Myosin,  144 
Myosinogen,  144 

N. 

Nails,  124 
matrix,  124 
root,  124 
Nasal  cavity,  231 
Near-point,  260 
Nerve-cells,  159,  162,  175 
ganglia,  159,  162 
salivary  secretion,  93 
-degeneration,   167,  177 

histologies!  changes,  168 
-endings,  163 

efferent  nerves,  163 
sensory  nerves,  163 
-fibres,  159 

centrifugal,  162 
centripetal,  162 
function,  161 
of  hemispheres,  197 
rnedullated,  159 
motor,  179,  203 
non-medullated,  159,  161 
of  Eemak,  161 
sensory,  179,  204 
of  sympathetic,  169 
-impulse,  165 
direction  of,  166 

experiments,  166 
nature  of,  165 
olfactory,  230 
origin,  230 
speed  of,  167 
-regeneration,  168 
-roots,  174,  176 
anterior,  174,  176 

course,  176 

degeneration,  167,  177 
posterior,  174,  176 

course,  176 
trophic  centres,  177 
-trunks,  161 

vaso-motor,  66,  173 
Nerves,  auditory,  238 
centres,  199 


Nerves,  cranial  (see  also  Cranial  nerves), 

206 

nuclei  of,  188 
nucleus,  238 
optic,  253 

fibres  of,  251,  253 
pneumogastric,  in  respiration,  86,217 

section  of,  87 
spinal,  174 
roots,  174 

Nervous  system,  159-220 
Neurilemma,  159,  160 
Neuroglia,  175 
Neuron,  164 

Nitrogen  in  atmosphere,  84 
Nitrogenous  equilibrium,  Io9 
Nodes  of  Eanvier.  160 
Nose,  231 
Nutrition,  136-138 

o. 

Odors,  229 
Olfactory  bulb,  231 

cells,  230 

nerves,  230 

tract,  231 

Olivary  bodies,  187 
Optagrams,  258 
Optic  chiasm,  253 

nerve  (see  also  Nerves,  optic),  253 
radiations,  253 

thalamus,  196,  198 

tracts,  253 
Organ  of  Corti,  238 
Organs,  23 
Osmosis,  111 
Ossicles,  234 
Ovaries,  270 

Graafian  follicles,  270 

strom a,  270 
Ovulation,  276 

connection  with  menstruation,  278 

frequency  of,  276 
Ovum,  271,  282 

constriction,  285 

unimpregnated,  276 

history  of,  276 
Oxidation,  18 
Oxygen,  137 

P. 

Pacinian  corpuscle,  164 
Pain,  181,  221 
Pancreas,  104 


320 


INDEX. 


Pancreas,  juice,  104 
composition,  105 
function,  106 
Paraglobulin,  41,  44 
Paraplegia,  201 
Parturition.  :soi> 

nature,  307 

time,  306 
Penis,  280 

erectile  tissue,  281 

glans,  280 
Pepsin,  97,  98,  105 
Pepsinogen,  98 
Peptones,  91).  li:; 
Perceptions,  222 

visual,  257 

mental  processes  of,  257 
Perilymph,  235,  239 
Perspiration,  122,  124 

amount.  1  -.'."> 

insensible,  125 

necessity,  126 

nervous  mechanism,  125 

odor,  125 

purpose,  125 
Placenta,  290 

appearance  of,  292 

destiny  of,  291 

foetal,  290 

layers  of  cells,  290 

maternal,  290 

period  of  formation,  292 
Place ntal  circulation  (sec  also  Circula- 
tion, plnceutal),  292,  294 
Plasma,  40 

of  muscle,  144 
Pleura,  77 
Plexus,  pelvic,  172 

solar,  172 
Polar  body,  277 
Pons  Varolii,  191 
Presbyopia,  261 
Primitive  groove,  285 

trace,  2S4 
Processes,  intermaxillary,  299 

maxillary,  •_'!>!> 
Pronucleus,  female,  277 

malr,  282 

Prostate  gland,  280 
Proteids,  28,  30 

albumins,  28 

fibrin,  28 

globulins,  28 

peptones,  28 

t<-sts  for,  309 
Proteolytic  action,  99 


Protoplasm,  19,  22 
Protovertebne,  298 
Proximate  principles,  25-29 
inorganic,  25,  26 
distribution,  26 
uses,  26 
organic,  25 
list  of,  28,  29 
nitrogenous,  27,  28 
non-nitrogenous,  27,  28 
source,  27 
uses,  27 
Puberty,  274 
Pulse,  68-70 
extinction,  69 
sphygmograph,  68 

tracings,  (>9 
varieties,  68 
venous,  54,  69 

Pyramidal  tracts,  177,  186,  203 
crossed,  1S6,  203 
direct,  186,  203 
Pyramids  of  medulla,  186 

B. 

Reflex  action  of  cord,  181,  182 

of  medulla,  188 
Refraction  (eye),  248,  249 
Rennin,  121 
Reproduction,  267-283 
methods  of,  267 

asexual,  2(>S 

sexual,  268,  269 
theory  of,  268 
Respiration.  75-90 
abdominal,  80 
act  of,  75 

associated  movements,  82 
automatic  impulses,  86 
centres,  86 

synchronism  of,  87 
effects  of,  on  circulation,  88 
expiration,  81 

muscles,  81 
external,  84 
force  of,  83 
forced,  81 
frequency,  82 
inspiration,  78-81 

muscles,  78 
internal.  >.", 
movements.  75 
nerves,  86 

nervous  mechanism,  85 
reflex  influences,  85 


INDEX. 


321 


Respiration  sounds,  82 
special  acts,  89 
sighing,  89 
sneezing,  89 
laughing,  etc.,  90 
thoracic,  80 
tract,  75 

Kestiform  body,  187 
Retina,  246,  250,  259 
inversion  of  image,  25(5 
pigment  of,  259 
Retinal  red,  257 

reflex,  258 
Rigor  mortis,  158 
causes  of,  159 
disappearance  of,  159 
Rima  glottidis,  241 
Rods,  251 

8. 

Saccule,  237 
Saliva,  92 
mixed,  92 
secretion,  93 

chorda  tympani,  93 
nerve-control,  93 
Saponification,  105 
Scala  media,  237 
tympani,  236 
vestibuli,  236 
Sclera,  246 
Sebaceous  glands,  122 

secretion,  125 
Secreting  glands,  116 
racemose,  116 
tubular,  116 
Secretion,  115-136 
correlation,  118 
discharge  of,  117 
milk,  120 
mucous,  118 
mucus,  118 
processes  of,  115,  116 
chemical,  117 
physical,  116 
serous,  118 

peritoneum,  118 
pleura.  118 
table  of,  136 
Segmentation,  283 

nucleus,  283 
Semicircular  canals,  235 
Seminal  cells,  279 

vesicles,  280 
Seminiferous  tubules,  279 

21— Phys. 


Sensations,  centres,  199 
classification,  221 
common,  221 
organs  necessary  for,  220 
pressure,  224 
special,  221 
visual,  256 

duration  of,  256 
Senses,  the,  220-265 
nerves  of,  222 
seat  of,  221 
special,  222 
muscle,  224 

centre,  225 
temperature,  225 
Sense-organs,  163 

Pacinian  corpuscles,  164 
touch-corpuscles,  164 
Sensibility,  tactile,  224 

variations,  224 
Serum,  41,  118 
-albumin,  41 
Sight,  243-265 
Skin,  121-124 
absorption  by,  126 
corium,  121,  122 
cuticle,  121 
cutis  vera,  121,  122 
derma,  121,  122 
epidermis,  121 
papillae,  122 
Smell,  229-232 
acuteness,  232 
conditions  for,  229 
Sneezing,  232 
Sodium  glycocholate,  107 

taurocholate,  107 
Somatopleure,  286,  288 
Somites,  mesoblastic,  298 
Sound-waves,  239 

course  of,  239 
Species,  267 
Speech,  241 
articulate,  242 

organs  used  in,  242 
centre,  199 
Spermatozoa,  279 
Spermatozoon,  281,  282 
Sphygmograph,  68 
Spinal  cord,  174-185 
augmentation,  184 
automatic  acts,  184 
columns,  175,  186 
anterior,  186 
lateral,  187 
posterior,  187 


322 


INDEX. 


Spinal  cord,  coordination,  184 
enlargements,  177 
functions,  178 

conduction,  178 
gray  matter,  175 
gross  anatomy,  174 
lesions,  203 

microscopic  examination,  175 
mutilations,  204 
recurrent-sensibility  fibres,  177 
reflex  action,  181,  182 

special  reflexes,  182 
transference,  181 
white  substance,  175 
Splanchnopleure,  286,  287,  288 
Spleen,  136 
Stapes,  234 
Starch,  tests  for,  310 
Starvation,  138 
Steapsin,  105 
Stercobilin,  109 
Stercorin,  109 
Stereoscope,  256 
Stomach,  94-99 

absorption  from,  101 

capacity,  100 

digestion,  gastric   (see  also   Gastric 

digestion),  100 
after  death,  101 
glands,  96 
peptic,  96 
pyloric,  96,  97 
muscular  action,  99 
structure,  94 
Stomata,  71 
Strabismus,  262 
external,  262 
internal,  262 
Succus  entericus,  104 
Sugar,  test  for,  310 
Sweat,  122,  124 

-glands,  122 

Sympathetic  system,  169-173 
function,  173 
ganglia,  169,  171-172 
abdominal,  172 
cephalic,  171 
cervical,  172 
thoracic,  172 

relation  to  secreting  glands,  173 
sensory  and  motor  influence,  173 
vaso-motor  fibres,  173 
Systole  (see  also  Heart),  61 


Taste,  ±ir>-£»J 


T. 


Taste,  after-,  229 

a.-v-MH-iatioi!  with  smell,  228 

-goblets,  227 

necessary  conditions  for,  225 

origin  of,  226 
Teeth,  91 

permanent,  91 

temporary,  91 
Temperature  of  body,  140 

srii>ations,  181 
Testicles,  279 

tubules,  279 

tunica  albuginea,  279 
Thoracic  duct,  70,  114 
Thymus,  136 
Thyroid,  136 
Tic  douloureux,  211 
Tissue,  23 
Tongue,  90,  226 

papillae,  226 

sensibility,  229 

taste-goblets,  227 

touch,  227 

varieties,  226 
Tonsils,  136 
Tooth,  91 

cavity,  92 

cement,  92 

crown,  91 

crusta  petrosa,  92 

dentine,  92 

enamel,  92 

fang,  91 

neck,  91 

pulp,  92 
Touch,  181,  222-225 

acuteness  of,  223 
measure  of,  223 

corpuscles,  164 

organ  of,  222 

varieties  of,  223 
Trachea,  76 
Tracts,  203,  204 

motor,  203 
lesions,  203,  204 

sensory,  204 
Trypsin,  105 
Tympanum,  233 

membrane,  233,  234 

u. 

Umbilical  arteries,  291,  296,  297 
cord,  291 
veins,  291 
vesicle,  287 


INDEX. 


323 


Urea,  134 
amount,  135 
as  a  waste,  135 
Ureters,  129 
pelvic,  129 
Urethra,  280 
Uric  acid,  135 
Urine,  129 
acidity,  131 

acid  sodium  phosphate,  131 
amount,  131 
coloring-matter,  130 
composition,  130 
course  in  tubules,  133 
estimation  of  solids,  135 
properties,  129 
secretion,  130 

conditions  affecting,  132 
epithelial  action,  130 
nitration,  130 

relation  to  arterial  pressure,  132 
Uriniferous  tubules,  127 

course,  127 
Uterine  sinuses,  290 
Uterus,  273 

contractions  of,  307 
causes,  307 
characters  of,  307 
Utricle,  237 

V. 

Valves  of  heart,  53 

of  veins,  55 

Valvulse  conniventes,  102,  111 
Vas  defereus,  279 
Veins,  55 

contraction,  57 

pulsation  of  jngular,  54 

size,  56 

structure,  55 


Veins,  valves,  55 

Ventricle,  fourth,  floor  of,  188 

of  heart,  51,  52 
action,  52 

lateral,  193 
Vesicles,  primary,  301,  302 

secondary,  301,  302 
Vestibule,  235,  237 
Villi,  111,  112 

structure,  112 
Vision,  area  of  most  acute,  252 

binocular,  255 

centre  for,  199 

clearness,  257 

nervous  mechanism  of,  255 
Vitelline  duct,  287 

membrane,  272 
Vitellus,  273,  287 
Vitreous  humor,  248 
Vocal  cords,  241 
Voice,  241 

musical  range  of,  242 

production,  241 
Vomiting,  101 

w. 

Waste-products,  18 
Whartou's  jelly,  291 
Wolffian  body,  305 
duct,  305 

Y. 

Yolk-sac,  287,  292 

Z. 

Zona  pellucida,  272 
Zymogen,  104 


CATALOGUE  OF  PUBLICATIONS  OF 

LEA    BROTHERS   &   COMPANY, 

706,  708  &  710  Saiisom  St.,  Philadelphia. 
Ill  Fifth  Ave.  (Cor.  18th  St.),  New  York. 

The  books  in  the  annexed  list  will  be  sent  by  mail,  post-paid,  to  any  Post-Office  in  the 
United  States,  on  receipt  of  the  printed  prices. 

INDEX. 

ANATOMY.    Gray,  p.  11  ;  Treves,  30  ;  Gerrish,  11;  Brockway,  4. 

DICTIONARIES.    Dunglison,  p.  8  ;  Duane,  8  ;  National,  4. 

PHYSICS.     Draper,  p.  8  ;  Robertson,  24  ;  Martin  &  Rockwell,  20. 

PHYSIOLOGY.     Foster,   p.  10;   Chapman,  5;   Schofield,  25;   Collins 
&  Rockwell,  6.  [Luff,  19  ;  Remsen,  24. 

CHEMISTRY.      Simon,  p.  26  ;  Attfield,  3  ;  Martin  &  Rockwell,  20; 

PHARMACY.    Caspari,  p.  5.  [Bruce,  4  :  Schleif,  25. 

MATERIA   MEDICA.     Culbretb,  p.  6  ;   Maisch,  19  ;   Farquharson,  9  ; 

DISPENSATORY.    National,  p.  21. 

THERAPEUTICS.      Hare,  p.  13  ;  Fothergill,  10  ;  Whitla,  31  ;  Hayem 
&  Hare,  14  ;  Bruce,  4  ;  Schleif,  25  ;  Cushny,  6. 

PRACTICE.     Flint,  p.  9  ;  Loomia  &  Thompson,  19  ;  Malsbary,  20. 

DIAGNOSIS.    Musser,  p.  21 ;  Hare,  12;  Simon,  25;  Herrick,  15;  Hutchi- 
son &  Rainey,  16  ;  Collins,  6. 

CLIMATOLOGY.    Solly,  p.  26  ;  Hayem  &  Hare,  14. 

NERVOUS  DISEASES.    Dercum,  p.  7  ;    Gray,  11 ;  Potts,  23. 

MENTAL  DISEASES.     Clouston,  p.  5  ;  Savage,  24  ;  Folsom,  10. 

BACTERIOLOGY.       Abbott,  p.  2 ;    Vaughan  &  Novy,  30  ;    Senn's 
(Surgical),  25.      Park,  22  ;  Coates,  6.  [Vale,  21. 

HISTOLOGY.    Klein,  p.  17  ;  Schafer's,  25  ;    Dunham,  8  ;  Nichols  & 

PATHOLOGY.    Green,  p.  12;  Gibbes,  10;  Coats,  6;  Nichols  &  Vale,  21. 

SURGERY.     Park,  p.  22;  Dennis,  7;  Roberts,  24;  Ashhurst,  3;  Treves, 29; 
Cheyne  &  Burghard,  5  ;  Gallaudet,  10. 

SURGERY— OPERATIVE.    Stimson,  p.  27  ;  Smith,  26  ;  Treves,  29. 

SURGERY— ORTHOPEDIC.    Young,  p.  31 ;  Gibney,  10. 

SURGERY— MINOR.    Wharton,  p.  30.  [Ballenger  & 

FRACTURES  and  DISLOCATIONS.   Stimson,  p.  27.  [Wippern,  3. 

OPHTHALMOLOGY.    Norris  &  Oliver,  p.  21 ;  Nettleship,  21;  Juler,  17; 

OTOLOGY.  Politzer,  p.  23;  Burnett,  5;  Field,  9;  Bacon,  4. 

LARYNGOLOGY  and  RHINOLOGY.  Coakley,  p.  6  ; 

DENTISTRY.    Essig  (Prosthetic),  p.  9  ;  Kirk  (Operative),  17  ;  Ameri- 
can System,  2  ;  Coleman,  6;  Burchard  4. 

URINARY  DISEASES.    Roberts,  p.  24  ;  Black,  4  ;  Morris,  20. 

VENEREAL    DISEASES.      Taylor,  p.  28  ;    Hayden,  14  ;    Cornil,  6  ; 
Likes,  19. 

SEXUAL  DISORDERS.    Fuller,  p.  10  ;  Taylor,  29. 

DERMATOLOGY.      Hyde,  p.  16  ;  Jackson,  16  ;  Pye-Smith,  24  ;  Mor- 
ris, 20  ;  Jamieson,  16 ;  Hardaway,  12  ;  Grindon,  12. 

GYNECOLOGY.      American  System,  p.  3  ;    Thomas   &  Munde",  29 
Emmet,  9  ;  Davenport,  7  ;  May,  20  ;  Dudley,  8  ;  Crockett,  6. 

OBSTETRICS.    American  System,  p.  3  ;   Davis,  7  ;  Parvin,  22  ;  Play- 
fair,  23  ;  King,  17  ;  Jewett,  17  ;  Evans,  9. 

PEDIATRICS.    Smith,  p.  26  ;  Thomson,  29  ;  Williams,  31  ;  Tattle,  30. 

HYGIENE.     Egbert,  p.  9  ;  Richardson,  24  ;  Coates,  6. 

MEDICAL  JURISPRUDENCE.    Taylor,  p.  28. 

QUIZ  SERIES,  POCKET  TEXT-BOOKS  and  MANUALS. 

Pp.  18,  25  and  27. 
9,1.9 


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ABBOTT  (A.  O.).  PRINCIPLES  OF  BACTERIOLOGY:  a  Practical 
Manual  for  Students  and  Physicians.  New  (5th)  edition  thoroughly 
revised  and  greatly  enlarged.  In  one  handsome  12mo.  vol.  of  585  pages, 
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One  of  its  most  attractive  charac- 
teristics is  that  the  directions  are  so 
clearly  given  that  anyone  with  a 
moderate  amount  of  laboratory  train- 
ing can,  with  a  little  care  as  to 
detail,  make  his  experiments  suc- 


cessfully. To  those  who  require  a 
condensed  yet  nevertheless  complete 
work  upon  Bacteriology  we  most 
cordially  recommend  it. — 
peutic  Gazette. 


AMERICAN  SYSTEM  OF  PRACTICAL  MEDICINE.  A  SYS- 
TEM OF  PRACTICAL  MEDICINE.  In  contributions  by  Various 
American  Authors.  Edited  by  ALFRED  L.  LOOMIS,  M.D.,  LL.D., 
and  W.  OILMAN  THOMPSON,  M.  D.  In  four  very  handsome  octavo 
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For  tale  by  subscription  only.  Prospectus  free  on  application. 


Every  chapter  is  a  masterpiece  of 
completeness,  and  is  particularly  ex- 
cellent in  regard  to  treatment,  many 
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charts  and  tables  being  given  for  the 
guidance  of  the  practitioner. 

"The  American  Svstem  of  Medi- 


cine" is  a  work  of  which  every 
American  physician  may  reasonably 
feel  proud,  and  in  which  every  prac- 
titioner will  find  a  safe  and  trust- 
worthy counsellor  in  the  daily  re- 
sponsibilities of  practice.  —  The  Ohio 
Medical  Journal. 


AMERICAN  SYSTEM  OF  DENTISTRY.  In  treatises  by  various 
authors.  Edited  by  WILBUR  F.  LITCH,  M.D.,  D.D.S.  In  three  very 
handsome  super-royal  octavo  volumes,  containing  about  3200  pages, 
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pectus free  on  application  to  the  Publishers. 

AMERICAN  TEXT-BOOKS  OF  DENTISTRY,  In  Contribu- 
tions by  Eminent  American  Authorities.  In  two  very  handsome 
octavo  volumes,  richly  illustrated  : 

PROSTHETIC  DENTISTRY.  Edited  by  CHARLES  J.  ESSIG,  M.D., 
D.D.S.,  Professor  of  Mechanical  Dentistry  and  Metallurgy,  Department 
of  Dentistry,  University  of  Pennsylvania,  Philadelphia.  760  pages, 
983  engravings.  Cloth,  $6 ;  leather,  $7.  Net. 

No  more  thorough  production  will  |  It  is  up  to  date  in  every  particular, 
be  found  either  in  this  country  or  in  (  It  is  a  practical  course  on  prosthetics 
any  country  where  dentistry  is  un-  which  any  student  can  take  up  dur- 
derstood  as  a  part  of  civilization. —  j  ing  or  after  college. — Dominion  Den- 
The  International  Dental  Journal.  \  tal  Journal. 

OPERATIVE  DENTISTRY.  Edited  by  EDWARD  C.  KIRK,  D.D.S., 
Professor  of  Clinical  Dentistry,  Department  of  Dentistry,  University 
of  Pennsylvania.  699  pages,  751  engravings.  Cloth,  $5.50;  leather, 
$6.50.  Net.  Just  ready. 


Written  by  a  number  of  practi- 
tioners as  well  known  at  the  chair 
as  in  journalistic  literature,  many  of 
them  teachers  of  eminence  in  our 
colleges.  It  should  be  included  in 
the  list  of  text-books  set  down  as 
most  useful  to  the  college  student.— 
The  Dental  News. 


It  is  replete  in  every  particular 
and  treats  the  subject  in  a  progressive 
manner.  It  is  a  book  that  every 
progressive  dentist  should  possess, 
and  we  can  heartily  recommend  it 
to  the  profession.— The  Ohio  Dental 
Journal. 


LEA  BROTHEKS  &  Co.,  PHILADELPHIA  AND  NEW  YOEK.      3 

AMERICAN  SYSTEMS  OF  GYNECOLOGY  AND  OBSTET- 
RICS. In  treatises  by  the  most  eminent  American  specialists.  Gyne- 
cology  edited  by  MATTHEW  D.  MANN,  A.  M.,  M.  D.,  a"d  Obstetrics 
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AMERICAN  TEXT-BOOK  OF  ANATOMY.     See  Gerrish,  page  11. 

ALLEN  (HARRISON).  A  SYSTEM  OF  HUMAN  ANATOMY; 
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A  PRACTICE  OF  OBSTETRICS  BY  AMERICAN  AU- 
THORS. See  Jewettj  page  17. 

A  TREATISE  ON  SURGERY  BY  AMERICAN  AUTHORS. 

FOR  STUDENTS  AND  PRACTITIONERS  OF  SURGERY  AND 
MEDICINE.  Edited  by  ROSWELL  PARK,  M.D.  See  page  22. 

ASHHURST  (JOHN,  JR.).  THE  PRINCIPLES  AND  PRACTICE 

OF  SURGERY.  For  the  use  of  Students  and  Practitioners.  Sixth 
and  revised  edition.  In  one  large  and  handsome  octavo  volume  of 
1161  pages,  with  656  engravings.  Cloth,  $6 ;  leather,  $7. 


As  a  masterly  epitome  of  what  has 
been  said  and  done  in  surgery,  as  a 
succinct  and  logical  statement  of  the 
principles  of  the  subject,  as  a  model 


text-book,  we  do  not  know  its  equal. 
It  is  the  best  single  text-book  of 
surgery  that  we  have  yet  seen  in  this 
country. — New  York  Post- Graduate. 


A  SYSTEM  OF  PRACTICAL  MEDICINE  BY  AMERICAN 
AUTHORS.  Edited  by  WILLIAM  PEPPER,  M.  D.,  LL.  D.  In  five 
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per  volume,  cloth,  $5 ;  leather  $6 ;  half  Russia,  $7.  Sold  by  subscrip- 
tion only.  Prospectus  free  on  application  to  the  Publishers. 

ATTFDELD  (JOHN).  CHEMISTRY ;  GENERAL,  MEDICAL  AND 
PHARMACEUTICAL.  New  (16th)  edition,  specially  revised  by  the 
Author  for  America.  In  one  handsome  12mo.  volume  of  784  pages, 
with  88  illustrations.  Cloth,  $2.50,  net. 

It  is  replete  with  the  latest  inform-  been  adopted,  bringing  the  work  into 
ation,  and  considers  the  chemistry  of  close  touch  with  the  latest  United 
every  substance  recognized  officially  States  Pharmacopoeia,  of  which  it  is 
or  in  general  practice.  The  modern  a  worthy  companion. — ThePittsburg 
scientific  chemical  nomenclature  has  Medical  Review. 

BALLENGER  (W.  L.)  AND  WIPPERN  (A.  G.).  Shortly.  A 
POCKET  TEXT-BOOK  OF  DISEASES  OF  THE  EYE,  EAR, 
NOSE  AND  THROAT.  In  one  handsome  12tno.  volume  of  about 
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Pocket  Text-books,  edited  by  BERN  B.  GALLAITDET,  M.  D.  See  p.  18. 

BARNES  (ROBERT  AND  FANCOURT).  A  SYSTEM  OF  OB- 
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231  illus.  Cloth,  $5 ;  leather,  $6. 


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An  intensely  practical  book  for  stu-    nal  of  Medicine. 

BARTHOLOW  (ROBERTS).  CHOLERA;  ITS  CAUSATION,  PRE- 
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BLACK  (D.  CAMPBELL).  THE  URINE  IN  HEALTH  AND 
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AND  PATHOLOGICALLY  CONSIDERED.  In  one  12mo.  volume 
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Concise,  practical,  clinical,  well 
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land Medical  Journal. 


A  concise,  yet  complete  manual, 
treating  of  the  subject  from  a  prac- 
tical and  clinical  standpoint.— The 
Ohio  Medical  Journal. 

BLOXAM  (C.  L.).  CHEMISTRY,  INORGANIC  AND  ORGANIC. 
With  Experiments.  New  American  from  the  fifth  London  edition. 
In  one  handsome  octavo  volume  of  727  pages,  with  292  illustrations. 
Cloth,  $2 ;  leather,  $3. 

BROCKWAY  (F.  J.).  A  POCKET  TEXT-BOOK  OF  ANATOMY. 
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BRUCE  (J.  MITCHELL).  MATERIA  MEDICA  AND  THERA- 
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PRINCIPLES  OF  TREATMENT.  In  one  octavo  volume.  Pre- 
paring. 

BRYANT  (THOMAS).  THE  PRACTICE  OF  SURGERY.  Fourth 
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of  1040  pages,  with  727  illustrations.  Cloth,  $6.50 ;  leather,  $7.50. 

BURCHARD  (HENRY  H.).  DENTAL  PATHOLOGY  AND  THER- 
APEUTICS. Handsome  octavo,  575  pages,  with  400  illustrations. 
Just  ready.  Cloth,  net,  $5.00 ;  leather,  net,  $6.00. 

In  the  treatment  of  the  subject  I  is  a  valuable  text-book  on  a  subject 
the  method  pursued  by  the  author  which  has  heretofore  not  been  ade- 
is  logical  ana  sequential.  The  work  I  quately  represented. -Dental  Cosmos. 


LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK.       5 

BURNETT  (CHARLES  H.)<  THE  EAR :  ITS  ANATOMY,  PHYSI- 
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Students  and  Practitioners.  Second  edition.  In  one  8vo.  volume  of 
580  pages,  with  107  illustrations.  Cloth,  $4 ;  leather,  $5. 

CARTER  (R.  BRUDENELL)  AND  FROST  (W.  ADAMS).  OPH- 
THALMIC SURGERY.  In  one  pocket-size  12mo.  volume  of  559 
pages,  with  91  engravings  and  one  plate.  Cloth,  $2.25.  See  Series  of 
Clinical  Manuals,  page  25. 

CASPARI   (CHARLES   JR.).     A  TREATISE  ON   PHARMACY. 

For  Students  and  Pharmacists.     In  one  handsome  octavo  volume  of 
680  pages,  with  288  illustrations.     Cloth,  $4.50. 

The  author's  duties  as  Professor  student  who  cannot  understand  must 
of  Theory  and  Practice  of  Pharmacy  be  dull  indeed.  The  book  is  full  of 
in  the  Maryland  College  of  Phar-  new,  clean,  sharp  illustrations, which 
macy,  and  his  contact  with  students  tell  the  story  frequently  at  a  glance, 
made  him  aware  of  their  exact  !  The  index  is  full  and  accurate. — 
wants  in  the  matter  of  a  manual,  j  National  Druggist. 
His  work  is  admirable,  and  the  i 

CHAPMAN  (HENRY  C.).  A  TREATISE  ON  HUMAN  PHYSI- 
OLOGY. New  (2d)  edition.  In  one  octavo  volume  of  921  pages, 
with  595  illustrations.  Just  ready.  Cloth,  $4.25 ;  leather,  $5.25,  net. 


In  every  respect  the  work  fulfils 
its  promise,  whether  as  a  complete 
treatise  for  the  student  or  as  an  ad- 


mirable work  of  reference  for  the 
physician. — North  Carolina  Medical 
Journal. 


CHARLES  (T.  CRANSTOUN).  THE  ELEMENTS  OF  PHYSIO- 
LOGICAL AND  PATHOLOGICAL  CHEMISTRY.  Octavo,  451 
pages,  with  38  engravings  and  1  colored  plate.  Cloth,  $3.50. 

CHEYNE  (W.  WATSON).  THE  TREATMENT  OF  WOUNDS, 
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Cloth,  $1.25. 


One  will  be  surprised  at  the 
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formation it  contains;  information 
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need  at  any  moment.  The  sections 
devoted  to  ulcers  and  abscesses  are 
indispensable  to  any  physician. — 
The  Charlotte  Medical  Journal. 


CHEYNE  (W.  W.)  AND  BURGH ARD  (F.  F.)  SURGICAL 
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CLARKE  (W.  B.)  AND  LOCKWOOD  (C.  B.).  THE  DISSECTOR'S 
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Cloth,  $1.50.  See  Students'  Series  of  Manuals,  page  27. 

CLELAND  (JOHN).  A  DIRECTORY  FOR  THE  DISSECTION  OF 
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CLINICAL  MANUALS.     See  Series  of  Clinical  Manuals,  page  25. 

CLOUSTON  (THOMAS  S.).  CLINICAL  LECTURES  ON  MENTAL 
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CLOWES  (FRANK).  AN  ELEMENTARY  TREATISE  ON  PRACTI- 
CAL CHEMISTRY  AND  QUALITATIVE  INORGANIC  ANALY- 
SIS. From  the  fourth  English  edition.  In  one  handsome  12mo. 
volume  of  387  pages,  with  55  engravings.  Cloth,  $2.50. 

COAKLEY  (COBNEJLIUS  G.).  THE  DIAGNOSIS  AND  TREAT- 
MENT OF  DISEASES  OF  THE  NOSE,  THROAT,  NASO- 
PHARYNX AND  TRACHEA.  In  one  12mo.  volume  of  about  400 
pages,  fully  illustrated.  Preparing, 

COATES  (W.  E.,  JR.).  A  POCKET  TEXT-BOOK  OF  BACTE- 
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about  350  pages,  with  many  illustrations.  Shortly.  Cloth,  $1.50,  net. 
Lea's  Series  of  Pocket  Test-books,  edited  by  BEKN  B.  GALT.AVDET, 
M.  D.  See  page  18. 

COATS  (JOSEPH).  A  TREATISE  ON  PATHOLOGY.  In  one  vol. 
of  829  pages,  with  339  engravings.  Cloth,  $5.50;  leather,  $6.50. 

COLEMAN  (ALFRED).  A  MANUAL  OF  DENTAL  SURGERY 
AND  PATHOLOGY.  With  Notes  and  Additions  to  adapt  it  to  Amer- 
ican Practice.  By  THOS.  C.  STELLWAGEN,  M.A.,  M.D.,  D.D.S.  In  one 
handsome  octavo  vol.  of  412  pages,  with  331  engravings.  Cloth,  $3.25. 

COLLINS  (C.  P.).  A  POCKET  TEXT-BOOK  OF  MEDICAL 
DIAGNOSIS.  In  one  handsome  12mo.  volume  of  about  350  PJI-.S, 
with  many  illustrations.  Shortly.  Cloth,$1.50,  net.  Lea? s  Series  of  P< ><•/;<( 
Text-books,  edited  by  BERN  B.  GALLAUDET,  M.  D.  See  page  18. 

COLLINS  (H.  D.)  AND  ROCKWELL  (W.  H.).  A  POCKET 
TEXT-BOOK  OF  PHYSIOLOGY.  In  one  handsome  12mo.  volume 
of  about  300  pages,  with  many  illustrations.  Cloth,  $1.50,  net.  In  pr<-s*. 
Lea's  Series  of  Pocket  Text-books,  edited  by  BERN  B.  GALLAUDET, 
M.  D.  See  page  18. 

CONDIE  (D.  FRANCIS).  A  PRACTICAL  TREATISE  ON  THE  DIS- 
EASES OF  CHILDREN.  Sixth  edition,  revised  and  enlarged.  In 
one  large  8vo.  volume  of  719  pages.  Cloth,  $5.25 ;  leather,  $6.25. 

CORNIL  (V.).  SYPHILIS:  ITS  MORBID  ANATOMY,  DIAGNO- 
SIS AND  TREATMENT.  Translated,  with  Notes  and  Additions,  by 
J.  HENRY  C.  SIMES,  M.D.  and  J.  WILLIAM  WHITE,  M.D.  In  one 
8vo.  volume  of  461  pages,  with  84  illustrations.  Cloth,  $3.75. 

CROCKETT  (M.  A.).  A  POCKET  TEXT-BOOK  OF  DISEASES 
OF  WOMEN.  In  one  handsome  12mo.  volume  of  about  350  pages, 
with  many  illustrations.  Cloth,$1.50,  net.  Shortly.  Lea's  Series  of  Pocket 
Test-books,  edited  by  BERN  B.  GALLAUDET,  M.  D.  See  page  18. 

CROOK  (JAMES  K.)  ON  MINERAL  WATERS  OF  THE 
UNITED  STATES.  Octavo,  575  pages.  Justready.  Cloth,  $3.50,  net. 

CULBRETH  (DAVID  M.  B.).  MATERIA  MEDICA  AND  PHAR- 
MACOLOGY. In  one  handsome  octavo  volume  of  812  pages,  with 
445  illustrations.  Cloth,  $4.75. 


A  thorough,  authoritative  and 
systematic  exposition  of  its  most 
important  domain.  —  The  Canada 
Lancet. 

This  work  ought  to  be  at  once 


adopted  as  the  text-book  in  all  col- 
leges of  pharmacy  and  medicine. 
It  is  one  of  the  most  valuable  works 
that  have  been  issued. — The  Ohio 
Medical  Journal. 


CUSHNY    (ARTHUR  B.).   TEXT-BOOK  OF  PHARMACOLOGY. 

Handsome  8vo.,  728  pages,  with  47  illus.  Just  ready.  Cloth,  $3.75,  net. 


LEA  BEOTHEBS  &  Co.,  PHILADELPHIA  AND  NEW  YORK.       7 


DAI/TON  (JOHN  C.).   A  TREATISE  ON  HUMAN  PHYSIOLOGY. 

Seventh  edition.  Octavo,  722  pages,  with  252  engravings.  Cloth, 
$5 ;  leather,  $6. 

DOCTRINES  OF  THE  CIRCULATION  OF  THE  BLOOD.  In 

one  handsome  12mo.  volume  of  293  pages.     Cloth,  $2. 

DAVENPORT  (F.  EL).      DISEASES  OF  WOMEN.     A  Manual  of 

Gynecology.  For  the  use  of  Students  and  Practitioners.  New 
(3d)  edition.  In  one  handsome  12mo.  volume  of  387  pages,  with  150 
illustrations.  Cloth,  $1.75,  net.  Just  ready. 

DAVIS  (EDWARD  P.).  A  TREATISE  ON  OBSTETRICS.  FOR 
STUDENTS  AND  PRACTITIONERS.  In  one  very  handsome 
octavo  volume  of  546  pages,  with  217  engravings  and  30  full-page 
plates  in  colors  and  monochrome.  Cloth,  $5 ;  leather,  $6. 

This  work  must  become  the  prac- 
titioner's text-book  as  well  as  the 
student's.  It  is  up  to  date  in  every 
respect. —  Va.  Med.  Semi- Monthly. 

A  work  unequalled  in  excellence. 
—  The  Chicago  Clinical  Review. 

Decidedly  one  of  the  best   text-    treatise  on  obstetrics.  —Med.  News. 

DAVIS  (F.  H.).  LECTURES  ON  CLINICAL  MEDICINE.  Second 
edition.  In  one  12mo.  volume  of  287  pages.  Cloth,  $1.75. 

DE  LA  HECHE'S  GEOLOGICAL  OBSERVER.  In  one  large  octavo 
volume  of  700  pages,  with  300  engravings.  Cloth,  $4. 

DENNIS  (FREDERIC  S.)  AND  BILLINGS  (JOHN  S.).  A  SYS- 
TEM OF  SURGERY.  In  contributions  by  American  Authors. 
Complete  work  in  four  very  handsome  octavo  volumes,  containing 
3652  pages,  with  1585  engravings  and  45  full-page  plates  in  colors 
and  monochrome.  Per  volume,  cloth,  $6.00;  leather,  $7.00;  half 
Morocco,  gilt  back  and  top,  $8.50.  For  sale  by  subscription  only. 
Full  prospectus  free  on  application  to  the  publishers. 


books  on  the  subject.  It  is  exception- 
ally useful  from  every  standpoint. — 
Nashville  Jour,  of  Med.  and  Surgery. 
From  a  practical  standpoint  the 
work  is  all  that  could  be  desired.  A 
thoroughly  scientific  and  brilliant 


It  is  worthy  of  the  position  which 
surgery  has  attained  in  the  great 
Republic  whence  it  comes.  —  The 
London  Lancet. 

It  may  be  fairly  said  to  represent 


American  surgery  and  is  thoroughly 
practical. — Annals  of  Surgery. 

No  work  in  English  can  be  con- 
sidered as  the  rival  of  this. — The 
American  Journal  of  the  Medical 


the    most    advanced    condition    of  j  Sciences. 

DERCUM  (FRANCIS  XM  EDITOR).  A  TEXT-BOOK  ON 
NERVOUS  DISEASES.  By  American  Authors.  In  one  handsome 
octavo  volume  of  1054  pages,  with  341  engravings  and  7  colored 
plates.  Cloth,  $6.00  ;  leather,  $7.00.  Net. 


Representing  the  actual  status  of 
our  knowledge  of  its  subjects,  and 
the  latest  and  most  fully  up-to-date 
of  any  of  its  class. — Jour,  of  Amer- 
ican Med.  Association. 

The  most  thoroughly  up-to-date 
treatise  that  we  have  on  this  subject. 
— American  Journal  of  Insanity. 


The  work  is  representative  of  the 
best  methods  of  teaching,  as  devel- 
oped in  the  leading  medical  colleges 
of  this  country. — Alienist  and  Neu- 
rologist. 

The  best  text-book  in  any  lan- 
guage.— The  Medical  Fortnightly. 


DE  SCHWE1NITZ  (GEORGE  E.).  THE  TOXIC  AMBLYOPIAS. 
Their  Classification,  History,  Symptoms,  Pathology  and  Treatment. 
Very  handsome  octavo,  240  pages,  46  engravings,  and  9  full-page 
plates  in  colors.  Limited  edition,  de  luxe  binding,  $4.  Net. 


8      LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK. 

DRAPER  (JOHN  O.).  MEDICAL  PHYSICS.  A  Text-book  for  Stu- 
dents and  Practitioners  of  Medicine.  In  one  handsome  octavo  volume 
of  734  pages,  with  376  engravings.  Cloth,  $4. 

DRUITT  (ROBERT).  THE  PRINCIPLES  AND  PRACTICE  OF 
MODERN  SURGERY.  A  new  American,  from  the  twelfth  London 
edition,  edited  by  STANLEY  BOYD,  F.  R.  C.  S.  In  one  large  octavo 
volume  of  965  pages,  with  373  engravings.  Cloth,  $4 ;  leather,  $5. 

DUANE  (ALEXANDER).  THE  STUDENT'S  DICTIONARY  OF 
MEDICINE  AND  THE  ALLIED  SCIENCES.  New  edition.  Com- 
prising the  Pronunciation,  Derivation  and  Full  Explanation  of  Medi- 
cal Terms,  with  much  Collateral  Descriptive  Matter.  Numerous  Tables, 
etc.  Square  octavo  of  658  pages.  Cloth,  $3.00;  half  leather,  $3.25; 
full  sheep,  $3.75.  Thumb-letter  Index,  50  cents  extra. 
Far  superior  to  any  dictionary  for  1  convenience  and  thoroughness.  — 

the  medical  student  that  we  know  of.    Medical  Record. 


—  Western  Med.  and  Surg.  Reporter. 
The  book  is  brought  accurately  to 


The  best  student's  dictionary. — 
Canada  Lancet. 


date.     It  is  a  model  of  conciseness, 

DUDLEY  (E.  C.).  THE  PRINCIPLES  AND  PRACTICE  OF 
GYNECOLOGY.  Handsome  octavo  of  652  pages,  with  422  illustra- 
tions in  black  and  colors.  Cloth,  $5.00,  net ;  leather,  $6.00,  net.  Just 
rtady. 


The  book   can  be  safely   recom- 
mended as  a  complete  and  reliable 


tice  of  modern  gynecology. — Inter- 
national Medical  Magazine. 


exposition  of  the  principles  and  prac- 
DUNCAN  (J.  MATTHEWS).    CLINICAL   LECTURES   ON   THE 
DISEASES  OF  WOMEN.  Delivered  in  St.  Bartholomew's  Hospital. 
In  one  octavo  volume  of  175  pages.    Cloth,  $1.50. 

DUNGLJSON  (ROBLEY).  A  DICTIONARY  OF  MEDICAL  SCI- 
ENCE.  Containing  a  full  explanation  of  the  various  subjects  and 
terms  of  Anatomy,  Physiology ;  Medical  Chemistry,  Pharmacy,  Phar- 
macology, Therapeutics,  Medicine,  Hygiene,  Dietetics,  Pathology,  Sur- 
gery, Ophthalmology,  Otology,  Laryngology,  Dermatology,  Gynecol- 
ogy, Obstetrics,  Pediatrics,  Medical  Jurisprudence,  Dentistry,  etc.,  etc. 
By  ROBLEY  DUNGLISON,  M.  D.,  LL.  D.,  late  Professor  of  Institutes 
or  Medicine  in  the  Jefferson  Medical  College  of  Philadelphia.  Edited 
by  RICHARD  J.  DUNGLISON,  A.  M.,  M.  D.  Twenty-first  edition,  thor- 
oughly revised  and  greatly  enlarged  and  improved,  with  the  Pronuncia- 
tion, Accentuation  and  Derivation  of  the  Terms.  With  Appendix. 
In  one  magnificent  imperial  octavo  volume  of  1225  pages.  Cloth,  $7  ; 
leather,  $8.  Thumb-letter  Index  for  quick  use,  75  cents  extra. 
The  most  satisfactory  and  authori- 1  scarcely  be  measured. — Med.  Record. 
tative  guide  to  the  derivation,  defini-  j  Pronunciation  is  indicated  by  the 
tion  and  pronunciation  of  medical  \  phonetic  system.  The  definitions  are 
terms.— The  Charlotte  Med.  Journal.  unusu&uy  ciear  and  concise.  The 


Covering  the  entire  field  of  medi- 
cine,   surgery    and    the    collateral 


book  is  wholly  satisfactory. —  Uni- 
versity Medical  Magazine. 


sciences,  its  range  of  usefulness  can 

DUNHAM  (EDWARD    K.).      MORBID    AND    NORMAL     HIS- 
TOLOGY.   Octavo,  450  pages,with  363  illustrations.  Cloth,  $3.25,  m-t. 
Just  ready. 
The  best  one- volume  text  or  refer-  I  of  published  in  America. —  Virginia 

ence  book  on  histology  that  we  know  I  Medical  Semi-Monthly. 

EDES  (ROBERT  T.).  TEXT-BOOK  OF  THERAPEUTICS  AND 
MATERIA  MEDICA.  In  one  8vo.  volume  of  544  pages.  Cloth,  $3.50  ; 
leather,  $4.50. 

EDIS  (ARTHUR  W.).  DISEASES  OF  WOMEN.  A  Manual  for 
Students  and  Practitioners.  In  one  handsome  8vo.  volume  of  576  pages, 
with  148  engravings.  Cloth,  $3 ;  leather,  $4. 


LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK.       9 

EGBERT  (SENECA).    A   MANUAL   OF  HYGIENE  AND  SANI- 
TATION.    In  one  12mo.  volume  of  359  pages,  with  63  illustrations. 
Just  ready.     Cloth,  Net,  $2.25. 
It  is   written  in  plain  language,  1  ligence.     The  writer  has  adapted  it 

and,  while  primarily  designed  for    to    American    conditions,   and    his 

physicians,  it  can  be  studied  with  j  suggestions  are,  above  all,  practical. 

profit  by  any  one  of  ordinary  Intel-  |  — The  New  York  Medical  Journal. 

ELL.IS  (GEORGE  VINER).  DEMONSTRATIONS  IN  ANATOMY. 
Eighth  edition.  Octavo,  716  pages,  with  249  engravings.  Cloth, 
$4.25 ;  leather,  $5.25. 

EMMET  (THOMAS  ADDIS).  THE  PRINCIPLES  AND  PRAC- 
TICE OF  GYNAECOLOGY.  Third  edition.  Octavo,  880  pages,  with 
150  original  engravings.  Cloth,  $5 ;  leather,  $6. 

ERICHSEN  (JOHN  E.).  THE  SCIENCE  AND  ART  OF  SUR- 
GERY. Eighth  edition.  In  two  large  octavo  volumes  containing 
2316  pages,  with  984  engravings.  Cloth,  $9  ;  leather,  $11. 

ESSIG  (CHARLES  J.).  PROSTHETIC  DENTISTRY.  See  American 
Text-Books  of  Dentistry,  page  2. 

EVANS  (DAVID  J.).  A  POCKET  TEXT-BOOK  OF  OBSTETRICS. 
In  one  handsome  12mo.  volume  of  about  300  pages,  with  many  illustra- 
tions. Cloth,  $1.50,  net.  Shortly.  Lea's  Series  of  Pocket  Text-books, 
edited  by  BERN  B.  GALLAUDET,  M.  D.  See  page  18. 

FARQUHARSON  (ROBERT).  A  GUIDE  TO  THERAPEUTICS. 
Fourth  American  from  fourth  English  edition,  revised  by  FRANK 
WOODBURY,  M.  D.  In  one  12mo.  volume  of  581  pages.  Cloth,  $2.50. 

FIELD  (GEORGE  P.).  A  MANUAL  OF  DISEASES  OF  THE 
EAR.  Fourth  edition.  In  one  octavo  volume  of  391  pages,  with  73 
engravings  and  21  colored  plates.  Cloth,  $3.75. 

To  those    who    desire    a  concise  j  It  is  just  such  a  work  as  is  needed 
work  on  diseases  of  the  ear,  clear   by    every    general    practitioner.  — 
and    practical,    this  manual    com-    American  Practitioner  and  News. 
mends  itself  in  the  highest  degree.  ' 

FLINT  (AUSTIN).    A   TREATISE   ON   THE  PRINCIPLES  AND 
PRACTICE   OF  MEDICINE.    Seventh  edition,  thoroughly  revised 
by  FREDERICK  P.  HENRY,  M.  D.    In  one  large  8vo.  volume  of  1143 
pages,  with  engravings.    Cloth,  $5.00 ;  leather,  $6.00. 
The  work  has  well  earned  its  lead-  {  medicine  in  the  medical  schools. — 
ing  place  in  medical  literature. —  j  Northwestern  Lancet. 


Medical  Record. 
The  leading  text-book  on  general 


The  best  of  American  text-books 
on  Practice. — Amer. Medico-Surgical 
Bulletin. 


—  A   MANUAL   OF  AUSCULTATION  AND  PERCUSSION ;  of 
the  Physical  Diagnosis  of  Diseases  of  the  Lungs  and  Heart,  and  of 
Thoracic  Aneurism.  Fifth  edition,  revised  by  JAMES  C.  WILSON,  M.  D. 
In  one  handsome  12mo.  volume  of  274  pages,  with  12  engravings. 

—  A    PRACTICAL    TREATISE    ON    THE    DIAGNOSIS    AND 
TREATMENT  OF  DISEASES  OF  THE  HEART.   Second  edition 
enlarged.     In  one  octavo  volume  of  550  pages.     Cloth,  $4. 

—  A   PRACTICAL  TREATISE   ON   THE  PHYSICAL  EXPLO- 
RATION  OF  THE   CHEST,  AND  THE  DIAGNOSIS  OF  DIS- 
EASES AFFECTING  THE  RESPIRATORY  ORGANS.    Second 
and  revised  edition.    In  one  octavo  volume  of  591  pages.  Cloth,  $4.50. 

—  MEDICAL  ESSAYS.  In  one  12mo.  vol.  of  210  pages.  Cloth,  $1.38. 

—  ON  PHTHISIS :  ITS  MORBID  ANATOMY.  ETIOLOGY,  ETC. 
A  Series  of  Clinical  Lectures.    In  one  8vo.  volume  of  442  pages. 
Cloth,  $3.50. 


10     LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK. 

FOLSOM    (C.  P.).      AN    ABSTRACT    OF   STATUTES    OF    U.  S. 

ON  CUSTODY  9F  THE  INSANE.    In  one  8vo.  vol.  of  108  pages. 

Cloth,  $1.50.    With  Clouston  on  Mental  Diseases  (new  edition,  see 

page  6)  $5.00,  net,  for  the  two  works. 
FORMULARY,  POCKET,  see  page  32. 

FOSTER  (MICHAEL.).  A  TEXT-BOOK  OF  PHYSIOLOGY.  New 
(6th)  and  revised  American  from  the  sixth  English  edition.  In  one 
large  octavo  volume  of  923  pages,  with  257  illustrations.  Cloth,  $4.50 ; 
leather,  $5.50. 

Unquestionably  the  best  book  that  i  This  single  volume  contains  all 
can  be  placed  in  the  student's  hands,  j  that  will  be  necessary  in  a  college 
and  as  a  work  of  reference  for  the  course,  and  all  that  the  physician 
busy  physician  it  can  scarcely  be  will  need  as  well. — Dominion  Med. 
excelled.— ThePhila.  Poly  clinic.  \  Monthly. 

FOTHERGILL  (J.  MILNER).  THE  PRACTITIONER'S  HAND- 
BOOK OF  TREATMENT.  Third  edition.  In  one  handsome  octavo 
volume  of  664  pages.  Cloth,  $3.75 ;  leather,  $4.75. 


clearly  stated,  cannot  fail  to  prove 
a  great  convenience  to  many  thought- 
ful but  busy  physicians.  The  prac- 


busy  p 
due  of 


tical  value  of  the  volume  is  greatly 
increased  by  the  introduction  of  many 
prescriptions — New  York  Med.  Jour. 


To  have  a  description  of  the 
normal  physiological  processes  of  an 
organ  and  of  the  methods  of  treat- 
ment of  its  morbid  conditions 
brought  together  in  a  single  chapter, 
and  the  relations  between  the  two 

FOWNES  (GEORGE).  A  MANUAL  OF  ELEMENTARY  CHEM- 
ISTRY (INORGANIC  AND  ORGANIC).  Twelfth  edition.  Em- 
bodying WATTS'  Physical  and  Inorganic  Chemistry.  In  one  royal 
12mo.  volume  of  1061  pages,  with  168  engravings,  and  1  colored 
plate.  Cloth,  $2.75 ;  leather,  $3.25. 

FRANKLAND  (E.)  AND  JAPP  (F.R.).  INORGANIC  CHEMISTRY. 
In  one  handsome  octavo  volume  of  677  pages,  with  51  engravings  and 
2  plates.  Cloth,  $3.75 ;  leather,  $4.75. 

FULLER  (EUGENE).  DISORDERS  OF  THE  SEXUAL  OR- 
GANS IN  THE  MALE.  In  one  very  handsome  octavo  volume  of 
238  pages,  with  25  engravings  and  8  full-page  plates.  Cloth,  $2. 


It  is  an  interesting  work,  and  one 
which,  in  view  of  the  large  and 
profitable  amount  of  work  done  in 
this  field  of  late  years,  is  timely  and 
well  needed. — Medical  Fortnightly. 

The  book  is  valuable  and  instruc- 


tive and  brings  views  of  sound 
pathology  and  rational  treatment  to 
many  cases  of  sexual  disturbance 
whose  treatment  has  been  too  often 
fruitless  for  good.  —  Annals  of 
Surgery. 


FULLER  (HENRY).  ON  DISEASES  OF  THE  LUNGS  AND  AIR 
PASSAGES.  Their  Pathology,  Physical  Diagnosis,  Symptoms  and 
Treatment.  From  second  English  edition.  In  one  8vo.  volume  of  475 
pages.  Cloth,  $3.50. 

GALLAUDET  (BERN  B.).  A  POCKET  TEXT-BOOK  ON  SUR- 
GERY. In  one  handsome  12mo.  volume  of  about  400  pages,  with  many 
illustrations.  Cloth,  $1.50,  net.  Shortly.  Lea's  Series  of  Pocket  Text- 
honks,  edited  by  BERN  B.  <  JAKLAUDKTJ  M.  D.  See  page  18. 

GANT  (FREDERICK  JAMES).  THE  STUDENT'S  SURGERY.  A 
M  ii  1 1  ii in  in  Parvo.  In  one  square  octavo  volume  of  845  pages,  with 
159  engravings.  Cloth,  $3.75. 

GIBBES  (HENEAGE).  PRACTICAL  PATHOLOGY  AND  MORBID 
HISTOLOGY.  Octavo,  314  pages,  with  60  illustrations.  Cloth,  $2.75. 

GD3NEY  (V.  P.).  ORTHOPEDIC  SURGERY.  For  the  use  of  Practi- 
tioners and  Students.  In  one  8vo.  vol.  profusely  illus.  Preparing. 


LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK.     11 


GERRISH  (FREDERIC  H.).  A  TEXT-BOOK  OF  ANATOMY. 
By  American  Authors.  Edited  by  Frederic  H.  Gerrish,  M.  D.  In  one 
imp.  octavo  volume  of  915  pages,  with  950  illustrations  in  black  and 
colors.  Just  ready.  Clth,$6.50;  flexible  waterproof,  $7;  leath.,$7.50,we£. 

In  this,  the  first  representative  treatise  on  Anatomy  produced  in  America, 
no  effort  or  expense  has  been  spared  to  unite  an  authoritative  text  with  the 
most  successful  anatomical  pictures  which  have  yet  appeared  in  the  world. 

The  editor  has  secured  the  co-operation  of  the  professors  of  anatomy  in 
leading  medical  colleges,  and  with  them  has  prepared  a  text  conspicuous 
for  its  simplicity,  unity  and  judicious  selection  of  such  anatomical  facts  as 
bear  on  physiology,  surgery  and  internal  medicine  in  the  most  compre- 
hensive sense  of  those  terms.  The  authors  have  endeavored  to  make  a 
book  which  shall  stand  in  the  place  of  a  living  teacher  to  the  student,  and 
which  shall  be  of  actual  service  to  the  practitioner  in  his  clinical  work, 
emphasizing  the  most  important  subjects,  clarifying  obscurities,  helping 
most  in  the  parts  most  difficult  to  learn,  and  illustrating  everything  by  all 
available  methods. 

GOULD  (A.  PEARCE).     SURGICAL  DIAGNOSIS.    In  one  12mo. 

vol.  of  589  pages.     Cloth,  $2.  See  Student's  Series  of  Manuals,  p.  27. 

GRAY  (HENRY).    ANATOMY,  DESCRIPTIVE  AND  SURGICAL. 

New  and  thoroughly  revised  American  edition,  much  enlarged  in  text, 
and  in  engravings  in  black  and  colors.  In  one  imperial  octavo  volume 
of  1239  pages,  with  772  large  and  elaborate  engravings  on  wood.  Price 
of  edition  with  illustrations  in  colors  :  cloth,  $7  ;  leather,  $8.  Price 
of  edition  with  illustrations  in  black :  cloth,  $6 ;  leather,  $7. 


This  is  the  best  single  volume 
upon  Anatomy  in  the  English 
language. —  University  Medical  Mag- 
azine. 

Gray's  Anatomy  affords  the  student 
more  satisfaction  than  any  other 
treatise  with  which  we  are  familiar. 
— Buffalo  Med.  Journal. 

The  most  largely  used  anatomical 
text-book  published  in  the  English 
language. — Annals  of  Surgery. 

Particular  stress  is  laid  upon  the 
practical  side  of  anatomical  teach- 


ing, and  especially  the  Surgical 
Anatomy. — Chicago  Med.  Recorder. 

Holds  first  place  in  the  esteem  of 
both  teachers  and  students. — The 
Brooklyn  Medical  Journal. 

The  foremost  of  all  medical  text- 
books.— Medical  Fortnightly. 

Gray's  Anatomy  should  be  the 
first  work  which  a  medical  student 
should  purchase,  nor  should  he  be 
without  a  copy  throughout  his  pro- 
fessional career. — Pittsburg  Medical 
Review. 


GRAY  (L.ANDON  CARTER).  A  TREATISE  ON  NERVOUS  AND 
MENTAL  DISEASES.  For  Students  and  Practitioners  of  Medicine. 
New  (2d)  edition.  In  one  handsome  octavo  volume  of  728  pages,  with 
172  engravings  and  3  colored  plates.  Cloth,  $4.75 ;  leather,  $5.76. 
An  up-to-date  text-book  upon  measures  which  are  often  the  physi- 


nervous  and  mental  diseases  com- 
bined. A  well-written,  terse,  ex- 
plicit, and  authoritative  volume 
treating  of  both  subjects  is  a  step  in 
the  direction  of  popular  demand. — 
The,  Chicago  Clinical  Review. 

"The  word  treatment,"  says  the 
author,  "  has  been  construed  in  the 
broadest  sense  to  include  not  only 
medicinal  and  non-medicinal  agents, 
but  also  those  hygienic  and  dietetic 


ciau's  best  reliance." — The  Journal 
of  the  American  Medical  Association. 
The  descriptions  of  the  various 
diseases  are  accurate  and  the  symp- 
toms and  differential  diagnosis  are 
set  before  the  student  in  such  a  way 
as  to  be  readily  comprehended.  The 
author's  long  experience  renders  his 
views  on  therapeutics  of  great  value. 
— The  Journal  of  Nervous  and  Men- 
tal Disease. 


12      LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK. 

GREEN  (T.  HENRY).  AN  INTRODUCTION  TO  PATHOLOGY 
AND  MORBID  ANATOMY.  New  (8th)  American  from  the  eighth 
London  edition.  In  one  handsome  octavo  volume  of  582  pages,  with 
216  engravings  and  a  colored  plate.  Cloth,  $2.50,  net.  Just  ready. 


A  work  that  is  the  text-book  of 
probably  four-fifths  of  all  the  stu- 
dents of  pathology  in  the  United 
States  and  Great  Britain  stands  in 
no  need  of  commendation.  The  work 
precisely  meets  the  needs  and  wishes 
of  the  general  practitioner. —  The 
American  Practitioner  and  News. 

Green's  Pathology  is  the  text-book 


of  the  day — as  much  so  almost  as 
Gray's  Anatomy.  It  is  fully  up-to- 
date  in  the  record  of  fact,  and  so  pro- 
fusely illustrated  as  to  give  to  each 
detail  of  text  sufficient  explanation. 
The  work  is  an  essential  to  the  prac- 
titioner— whether  as  surgeon  or  phys- 
ician. It  is  the  best  of  up-to  date 
text-books. —  Virginia  Med.  Monthly. 


GREENE  (WILLIAM  H.).  A  MANUAL  OF  MEDICAL  CHEM- 
ISTRY. For  the  Use  of  Students.  Based  upon  BOWMAN'S  Medical 
Chemistry.  In  one  12mo.  vol.  of  310  pages,  with  74  illus.  Cloth,  $1.75. 

GROSS  (SAMUEL  D.).  A  PRACTICAL  TREATISE  ON  THE  DIS- 
EASES, INJURIES  AND  MALFORMATIONS  OF  THE  URINARY 
BLADDER,  THE  PROSTATE  GLAND  AND  THE  URETHRA. 
Third  edition.  Octavo,  574  pages,  with  170  illustrations  Cloth,  $4.50. 

GRINDON  (JOSEPH).  A  POCKET  TEXT-BOOK  OF  SKIN 
DISEASES.  In  one  handsome  12mo.  volume  of  350  pages,  with 
many  illustrations.  Shortly.  Cloth,  $1.50,  net.  Lea's  Seri<*  <>f  P,,,-l-,t 
Text-books,  edited  by  BERN  B.  GALLATJDET,  M.  D.  See  page  18. 

HABERSHON  (S.  O.).  ON  THE  DISEASES  OF  THE  ABDOMEN 
Second  American  from  the  third  English  edition.  In  one  octavo  vol- 
ume of  554  pages,  with  11  engravings.  Cloth,  $3.50. 

HALL  (WINFIELD  S.)  TEXT-BOOK  OF  PHYSIOLOGY.  Octavo 
about  500  pages,  richly  illustrated.  In  press. 

HAMILTON  (ALLAN  MCLANE).  NERVOUS  DISEASES,  THEIR 
DESCRIPTION  AND  TREATMENT.  Second  and  revised  edition. 
In  one  octavo  volume  of  598  pages,  with  72  engravings.  Cloth,  $4. 

HARDAWAY  (W.  A.).  MANUAL  OF  SKIN  DISEASES.  New  (2d) 
edition.  In  one  12mo.  volume  of  560  pages,  with  40  illustrations  and 
2  plates.  Cloth,  $2.25,  net.  Just  ready. 


The  best  of  all  the  small  books  to 
recommend  to  students  and  practi- 
tioners. Probably  no  one  of  our 
dermatologists  has  had  a  wider  every- 


day clinical  experience.  His  great 
strength  is  in  diagnosis, descriptions 
of  lesions  and  especially  in  treat- 
ment.— Indiana  Medical  Journal. 


HARE  (HOB ART  AMORY).  PRACTICAL  DIAGNOSIS.  THE 
USE  OF  SYMPTOMS  IN  THE  DIAGNOSIS  OF  DISEASE.  New 
(4th)  edition.  In  one  octavo  volume  of  623  pages,  with  205  engravings 
and  14  full-page  colored  plates.  Cloth,  $5.00,  net.  Jtmt  r,  <>,/>/. 

It  is  unique  in  many  respects,  and  he  will  become  a  better  diaguosti- 
the  author  has  introduced  radical  cian.  This  is  a  companion  to  /Vac- 
changes  which  will  be  welcomed  by  |  tical  Therapeutics,  by  the  same 
alJ.  Anyone  who  reads  this  book  i  author,  and  it  is  difficult  to  conceive 
will  become  a  more  acute  observer,  of  any  two  works  of  greater  practical 
will  pay  more  attention  to  the  simple  utility.— Medical  Review. 
yet  indicative  signs  of  disease,  and 


LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK.     13 


HARE  (HOBART  AMORY).    A   TEXT-BOOK  OF  PRACTICAL 

THERAPEUTICS,  with  Special  Reference  to  the  Application  of  Reme- 
dial Measures  to  Disease  and  their  Employment  upon  a  Rational 
Basis.  With  articles  on  various  subjects  by  well-known  specialists. 
New  (7th)  and  revised  edition.  In  one  octavo  volume  of  776  pages. 
Cloth,  $3.75,  net;  leather,  $4.50,  net. 


Its  classifications  are  inimitable, 
and  the  readiness  with  which  any- 
thing can  be  found  is  the  most  won- 
derful achievement  of  the  art  of  in- 
dexing. This  edition  takes  in  all 
the  latest  discovered  remedies. — 
The  St.  Louis  Clinique. 

The  great  value  of  the  work  lies 
in  the  fact  that  precise  indications 
for  administration  are  given.  A 
complete  index  of  diseases  and 
remedies  makes  it  an  easy  reference 
work.  It  has  been  arranged  so  that 


it  can  be  readily  used  in  connection 
with  Hare's  Practical  Diagnosis. 
For  the  needs  of  the  student  and 
general  practitioner  it  has  no  equal. 
— Medical  Sentinel. 

The  best  planned  therapeutic  work 
of  the  century. — American  Prac- 
titioner and  News. 

It  is  a  book  precisely  adapted  to 
the  needs  of  the  busy  practitioner, 
who  can  rely  upon  finding  exactly 
what  he  needs. — The  National  Med- 
ical Review. 


HARE  (HOBART  AMORY)  ON  THE  MEDICAL  COMPLICA 
TIONS  AND  SEQUELAE  OF  TYPHOID  FEVER.  Octavo,  276 
pages,  21  engravings  and  two  full-page  plates.  Just  ready.  Cloth, 
$2.40,  net. 

A  very  valuable  production.  One 
of  the  very  best  products  of  Dr. 
Hare  and  one  that  every  man  can 


read  with  great  profit. — Cleveland 
Journal  of  Medicine. 


HARE  (HOBART  AMORY,  EDITOR).  A  SYSTEM  OF  PRAC- 
TICAL THERAPEUTICS.  In  a  series  of  contributions  by  eminent 
practitioners.  In  four  large  octavo  volumes  comprising  about  4500 
pages, with  about  550  engravings.  Vol.  IV.,  just  ready.  For  sale  by  sub- 
scription only.  Full  prospectus  free  on  application  to  the  Publishers. 
Regular  price,  Vol.  IV.,  cloth,  $6 ;  leather,  $7 ;  half  Russia,  $8. 
Price  Vol.  IV.  to  former  or  new  subscribers  to  complete  work,  cloth, 
$5  ;  leather,  $6 ;  half  Russia,  $7.  Complete  work,  cloth,  $20 ;  leather, 
$24 ;  half  Russia,  $28. 

The  great  value  of  Hare's  System  of  Practical  Therapeutics  has  led  to  a 
widespread  demand  for  a  new  volume  to  represent  advances  in  treatment 
made  since  the  publication  of  the  first  three.  More  than  fulfilling  this 
request  the  Editor  has  secured  contributions  from  practically  a  new  corps 
of  equally  eminent  authors,  so  that  entirely  fresh  and  original  matter  is 
ensured.  The  plan  of  the  work,  which  proved  so  successful,  has  been  fol- 
lowed in  this  new  volume,  which  will  be  found  to  present  the  latest  devel- 
opments and  applications  of  this  most  practical  branch  of  the  medical  art. 
The  entire  System  is  an  unrivalled  encyclopaedia  on  the  practical  parts  of 
medicine,  and  merits  the  great  success  it  has  won  for  that  reason. 


14     LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK. 


HARTSHORNE  (HENRY).  ESSENTIALS  OF  THE  PRINCIPLES 
AND  PRACTICE  OF  MEDICINE.  Fifth  edition.  In  one  12mo. 
volume,  669  pages,  with  144  engravings.  Cloth,  $2.75 . 

A  HANDBOOK  OF  ANATOMY  AND  PHYSIOLOGY.    In  one 

12mo.  volume  of  310  pages,  with  220  engravings.    Cloth,  $1.75. 

A  CONSPECTUS  OF  THE  MEDICAL  SCIENCES.    Comprising 

Manuals  of  Anatomy,  Physiology,  Chemistry,  Materia  Medica,  Prac- 
tice of  Medicine,  Surgery  and  Obstetrics.  Second  edition.  In  one  royal 
12mo.  vol.  of  1028  pages,  with  477  iUus.  Cloth,  $4.25 ;  leather,  $5. 

HAYDEN  (JAMES  B.).  A  MANUAL  OF  VENEREAL  DISEASES. 
New  (2d)  edition.  In  one  12mo.  volume  of  304  pages,  with  54  en- 
gravings. Cloth,  $1.50,  net.  Just  ready. 


It  is  practical,  concise,  definite 
and  of  sufficient  fulness  to  be  satis- 
factory.— Chicago  Clinical  Review. 

This  work  gives  all  of  the  prac- 
tically essential  information  about 
the  three  venereal  diseases,  gon- 
orrhoea, the  chancroid  and  syphilis. 
In  diagnosis  and  treatment  it  is  par- 


ticularly thorough,  and  may  be 
relied  upon  as  a  guide  in  the  man- 
agement of  this  class  of  diseases.— 
Northwestern  Lancet. 

It  is  well  written,  up  to  date,  and 
will  be  found  very  useful. — Inter- 
national Medical  Magazine. 


HAYEM  (GEORGES)  AND  HARE  (H.  A.).  PHYSICAL  AND 
NATURAL  THERAPEUTICS.  The  Remedial  Use  of  Heat,  Elec- 
tricity, Modifications  of  Atmospheric  Pressure,  Climates  and  Mineral 
Waters.  Edited  by  Prof.  H.  A.  HARE,  M.  D.  In  one  octavo  volume 
of  414  pages,with  113  engravings.  Cloth,  $3. 


This  well-timed  up-to-date  volume 
is  particularly  adapted  to  the  re- 
quirements of  the  general  practi- 
tioner. The  section  on  mineral 
waters  is  most  scientific  and  prac- 
tical. Some  200  pages  are  given  up 
to  electricity  and  evidently  embody 
the  latest  scientific  information  on 
the  subject.  Altogether  this  work 
is  the  clearest  and  most  practical  aid 
to  the  study  of  nature's  therapeutics 
that  has  yet  come  under  our  obser- 
vation.— The  Medical  Fortnightly. 

For  many  diseases  the  most  potent 
remedies  lie  outside  of  the  materia 
medica,  a  fact  yearly  receiving  wider 


recognition.  Within  this  large 
range  of  applicability,  physical 
agencies  when  compared  with  drugs 
are  more  direct  and  simple  in  their 
results.  Medical  literature  has  long 
been  rich  in  treatises  upon  medical 
agents,  but  an  authoritative  work 
upon  the  other  great  branch  of 
therapeutics  has  until  now  been  a 
desideratum.  The  section  on  climate, 
rewritten  by  Prof.  Hare,  will,  for 
the  first  time,  place  the  abundant 
resources  of  our  country  at  the  in- 
telligent command  of  American 
practitioners.  —  The  Kansas  City 
I  Medical  Index. 


HERMAN  (G.  ERNEST).  FIRST  LINES  IN  MIDWIFERY.  In 
one  12mo.  vol.  of  198  pages,  with  80  engravings.  Cloth,  $1.25.  See 
Student's  Series  of  Manuals,  page  27. 


HERMANN  (Li.).  EXPERIMENTAL  PHARMACOLOGY.  A  Hand- 
book of  the  Methods  for  Determining  the  Physiological  Actions  of 
Drugs.  Translated  by  ROBERT  MEADE  SMITH,  M.  D.  In  one  12mo, 
volume  of  199  pages,  with  32  engravings.  Cloth,  $1.50. 


LEA  BROTHEBS  &  Co.,  PHILADELPHIA  AND  NEW  YORK.     15 


HERRICK  (JAMES  B.).    A  HANDBOOK  OF  DIAGNOSIS.    In 

one  handsome  12mo.  volume  of  429  pages,  with  80  engravings  and  2 
colored  plates.    Cloth,  $2.50. 


Excellently  arranged,  practical, 
concise,  up-to-date,  and  eminently 
well  fitted  for  the  use  of  the  prac- 
titioner as  well  as  of  the  student. — 
Chicago  Med.  Recorder. 

This  volume  accomplishes  its  ob- 
jects more  thoroughly  and  com- 
pletely than  any  similar  work  yet 
published.  Each  section  devoted  to 
diseases  of  special  systems  is  pre- 
ceded with  an  exposition  of  the 
methods  of  physical,  chemical  and 


microscopical  examination  to  be  em- 
ployed in  each  class.  The  technique 
of  blood  examination,including  color 
analysis,  is  very  clearly  stated. 
Uranalysis  receives  adequate  space 
and  care. — New  York  Med.  Journal. 
We  commend  the  book  not  only  to 
the  undergraduate,  but  also  to  the 
physician  who  desires  a  ready  means 
of  refreshing  his  knowledge  of  diag- 
nosis in  the  exigencies  of  professional 
life. — Memphis  Medioal  Mo 


HILL   (BERKELEY).    SYPHILIS  AND  LOCAL    CONTAGIOUS 

DISORDERS.    In  one  8vo.  volume  of  479  pages.    Cloth,  $3.25. 

HILLDER  (THOMAS).  A  HANDBOOK  OF  SKIN  DISEASES. 
Second  edition.  In  one  royal  12mo.  volume  of  353  pages,  Avith  two 
plates.  Cloth,  $2.25. 

HIRST  (BARTON  C.)  AND  PIERSOL  (GEORGE  A.).  HUMAN 

MONSTROSITIES.  Magnificent  folio,  containing  220  pages  of  text 
and  illustrated  with  123  engravings  and  39  large  photographic  plates 
from  nature.  In  four  parts,  price  each,  $5.  Limited  edition.  For  sale 
by  subscription  only. 

HOBLYN  (RICHARD  D.).  A  DICTIONARY  OF  THE  TERMS 
USED  IN  MEDICINE  AND  THE  COLLATERAL  SCIENCES. 
In  one  12mo.  volume  of  520  double-columned  pages.  Cloth,  $1.50 ; 
leather,  $2. 

HODGE  (HUGH  L.).  ON  DISEASES  PECULIAR  TO  WOMEN, 
INCLUDING  DISPLACEMENTS  OF  THE  UTERUS.  Second  and 
revised  edition.  In  one  8vo.  vol.  of  519  pp.,  with  illus.  Cloth,  $4.50. 

HOFFMANN  (FREDERICK)  AND  POWER  (FREDERICK  B.). 

A  MANUAL  OF  CHEMICAL  ANALYSIS,  as  Applied  to  the 
Examination  of  Medicinal  Chemicals  and  their  Preparations.  Third 
edition,  entirely  rewritten  and  much  enlarged.  In  one  handsome  octavo 
volume  of  621  pages,  with  179  engravings.  Cloth,  $4.25. 

HOLMES  (TIMOTHY).  A  TREATISE  ON  SURGERY.  Its  Prin- 
ciples and  Practice.  A  new  American  from  the  fifth  English  edition. 
Edited  by  T.  PICKERING  PICK,  F.R.C.S.  In  one  handsome  octavo  vol- 
ume of  lOOS.pages,  with  428  engravings.  Cloth,  $6 ;  leather,  $7. 


—  A  SYSTEM  OF  SURGERY.  With  notes  and  additions  by  various 
American  authors.  Edited  by  JOHN  H.  PACKARD,  M.  D.  In  three 
very  handsome  8vo.  volumes  containing  3137  double-columned  pages, 
with  979  engravings  and  13  lithographic  plates.  Per  volume,  cloth,  $6 ; 
leather,  $7 ;  half  Russia,  $7.50.  For  tale  by  tubscription  only. 


16     LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK. 

HORNER  (WILLIAM  E.).  SPECIAL  ANATOMY  AND  HIS- 
TOLOGY.  Eighth  edition,  revised  and  modified.  In  two  large  8vo. 
volumes  of  1007  pages,  containing  320  engravings.  Cloth,  $6. 


HUDSON  (A.).  LECTURES  ON  THE  STUDY  OF  FEVER.    In  one 
octavo  volume  of  308  pages.    Cloth,  $2.50. 


HUTCHISON  (ROBERT)  AND  RAINY  (HARRY).  CLINICAL 
METHODS.  A  GUIDE  TO  THE  PRACTICAL  STUDY  OF 
MEDICINE.  In  one  12mo.  volume  of  562  pages,  with  137  engrav- 
ings and  8  colored  plates.  Cloth,  $3.00. 


A  comprehensive,  clear  and  re- 
markably up-to-date  guide  to  clinical 
diagnosis.  The  illustrations  are 
plentiful  and  excellent.  As  exam- 
ples of  the  more  recent  additions  to 


medical  knowledge  which  receive 
recognition,  we  mention  Widal's 
test  for  typhoid  and  the  Neuron 
theory  of  the  nervous  system. — 
Montreal  Medical  Journal. 


HUTCHINSON  (JONATHAN).  SYPHILIS.  In  one  pocket-size  12mo. 
volume  of  542  pages,  with  8  chromo-lithographic  plates.  Cloth,  $2.25. 
See  Series  of  Clinical  Manuals,  p.  25. 


HYDE  (JAMES  NEVINS).  A  PRACTICAL  TREATISE  ON  DIS- 
EASES OF  THE  SKIN.  New  (4th)  edition,  thoroughly  revised. 
In  one  octavo  volume  of  815  pages,  with  110  engravings  and  12  full- 
page  plates,  4  of  which  are  colored.  Cloth,  $5.25 ;  leather,  $6.25. 


This  edition  has  been  carefully  re- 
vised, and  every  real  advance  has 
been  recognized.  The  work  answers 
the  needs  of  the  general  practitioner, 
the  specialist,  and  the  student. — The 
Ohio  Med.  Jour. 

A  treatise  of  exceptional  merit 
characterized  by  conscientious  care 
and  scientific  accuracy. — Buffalo 
Med.  Journal. 

A  complete  exposition  of  our 
knowledge  of  cutaneous  medicine  as 
it  exists  to-day.  The  teaching  in- 
culcated throughout  is  sound  as  well 


as  practical.— The  American  Jour- 
nal of  the  Medical  Sciences. 

It  is  the  best  one-volume  work 
that  we  know.  The  student  who 
gets  this  book  will  find  it  a  useful 
investment,  as  it  will  well  serve  him 
when  he  goes  into  practice. —  Vir- 
ginia Medical  Semi-Monthly. 

A  full  and  thoroughly  modern 
text-book  on  dermatology.  —  The 
Pittsburg  Medical  Review. 

It  is  the  most  practical  hand- 
book on  dermatology  with  which  we 
are  acquainted.— The  Chicago  Med- 
ical Recorder. 


JACKSON  (GEORGE  THOMAS).  THE  READY-REFERENCE 
HANDBOOK  OF  DISEASES  OF  THE  SKIN.  New  (3d)  edition. 
In  one  12mo.  volume  of  637  pages,  with  75  illustrations  and  a  colored 
plate.  Just  ready.  Cloth,  $2.50,  nff. 


Asa  student's  manual,  it  may  be 
considered  beyond  criticism.  The 
book  is  singularly  full.— St.  Louis 
(t»d  Surgical  Journal. 


Without  doubt  forms  one  of  the 
best  guides  for  the  beginner  in  der- 
matology that  is  to  be  found  in  the 
English  language. — Medic  inc. 


JAMIESON  (W.  AJLL.AN).  DISEASES  OF  THE  SKIN.  Third 
edition.  In  one  octavo  volume  of  656  pages,  with  1  engraving  afld  9 
double-page  chromo-lithographic  plates,  Cloth,  $6, 


LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK.     17 


JEWETT  (CHARLES).  ESSENTIALS  OF  OBSTETRICS.    In  one 

12mo.  volume  of  356  pages,  with  80  engravings  and  3  colored  plates. 

Cloth ,  $2 . 25.    Just  ready. 

An  exceedingly  useful  manual  for  ing  it  in  attractive  and  easily  tangi- 
student  and  practitioner.  The  au-  ble  form.  The  book  is  well  illus- 
thor  has  succeeded  unusually  well  trated  throughout. — Nashville  Jour. 
in  condensing  the  text  and  in  arrang-  of  Medicine  and  Surgery. 


American    Authors. 

One  large  octavo  volume  of  763  pages,  with  441  engravings  in  black 
and   colors,  and    22  full-page  colored   plates.    Just  ready.    Cloth, 


THE  PRACTICE  OF  OBSTETRICS.     By 

ith  441 


$5.00,  net;  leather,  $6.00,  net. 
A  clear  and  practical  treatise  upon 
obstetrics  by  well-known  teachers  of 
the  subject.  A  special  feature  of 
this  work  would  seem  to  be  the 
excellent  illustrations  with  which 


the  book  abounds.  The  work  is 
sure  to  be  popular  with  medical 
students,  as  well  as  being  of  extreme 
value  to  the  practitioner.  —  The 
Medical  Age. 


JONES  (C.  HANDF1EL.D).  CLINICAL  OBSERVATIONS  ON 
FUNCTIONAL  NERVOUS  DISORDERS.  Second  American  edi- 
tion. In  one  octavo  volume  of  340  pages.  Cloth,  $3.25. 

JULER  (HEXRY).  A  HANDBOOK  OF  OPHTHALMIC  SCIENCE 
AND  PRACTICE.  Second  edition.  In  one  octavo  volume  of  549 
pages,  with  201  engravings,  17  chromo-lithographic  plates,  test-types  of 
Jaeger  and  Siiellen,  and  Holmgren's  Color-Blindness  Test.  Cloth, 
$5.50  ;  leather,  $6.50. 

The  volume  is  particularly  rich  in  |  color  blindness,  etc.    The   sections 
matter  of  practical  value,  such  as  |  devoted  to  treatment  are  singularly 
directions   for    diagnosing,    use    of   full  and  concise.  —  Medical  Age. 
instruments,  testing  for  glasses,  for  | 

KING  (A.  F.  A.).  A  MANUAL  OF  OBSTETRICS.  Seventh  edition. 
In  one  12mo.  volume  of  573  pages,  with  223  illustrations.  Cloth, 
$2.50. 

From  first  to  finish  it  is  thoroughly  j  cyclopedias.        The     well-arranged 
ractical,  concise  in  expression,  well    index    renders  the   book  useful  to 


illustrated,  and  includes  a  statement 
of  nearly  every  fact  of  importance 


the  practitioner  who  is  in  haste  to 
refresh    his     memory.  —   Virginia 


discussed  in    obstetric    treatises  or  !  Medical  Semi-Monthly. 

KIRK  (EDWARD  C.).  OPERATIVE  DENTISTRY.  Handsome 
octavo  of  700  pages,  with  751  illustrations.  Just  ready.  See  American 
Text-Books  of  Dentistry,  page  2. 


We  have  only  the  highest  praise 
for  this  valuable  work.  It  is  replete 
in  every  particular,  and  surpasses 
anything  of  the  kind  heretofore  at- 


tempted. We  can  heartily  recom- 
mend it  to  the  profession. — The 
Ohio  Dental  Journal. 


KLEIN  (E.).  ELEMENTS  OF  HISTOLOGY.  New  (5th)  edition.  In 
one  12mo.  volume  of  506  pages,  with  296  engravings.  Just  ready. 
Cloth,  $2.00,  net.  See  Student's  Series  of  Manuals,  page  27. 

This  work  deservedly  occupies  a 


It  is  the  most  complete  and  con- 
cise work  of  the  kind  that  has  yet 
emanated  from  the  press. — The  Med- 
ical Age. 


first  place  as  a  text-book  on  his- 
tology.— Canadian  Practitioner. 


18     LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK. 

L.ANDIS  (HENRY  G.).  THE  MANAGEMENT  OF  LABOR.  In  one 
handsome  12mo.  volume  of  329  pages,  with  28  illus.  Cloth,  $1.75. 

LiA  ROCHE  (R.).  YELLOW  FEVER.  In  two  8vo.  volumes  of  1468 
pages.  Cloth,  $7. 

LAURENCE  (J.  Z.)  AND  MOON  (ROBERT  C.).  A  HANDY- 
BOOK  OF  OPHTHALMIC  SURGERY.  Second  edition.  In  one 
octavo  volume  of  227  pages,  with  66  engravings.  Cloth,  $2.75. 

LEA'S  SERIES  OP  POCKET  TEXT-BOOKS,  edited  by  BKRN 
B.  GALLAUDET,  M.  D.  Covering  the  entire  field  of  Medicine  in  a 
series  of  16  very  handsome  cloth-bound  12mo.  volumes  of  350-450 
pages  each,  profusely  illustrated.  Compendious,  clear,  trustworthy  and 
modern,  and  issued  at  the  very  moderate  price  of  $1.50,  net,  per 
volume.  The  following  volumes  constitute  the  series. 

Co ATES' Bacteriology  and  Hygiene.  BROCKWAY'S  Anatomy.  COM  .INS 
and  ROCKWELL'S  Physiology.  MARTIN  and  ROCKWELL'S  <  'hemistry 
and  Physics.  NICHOLS  and  VALE'S  Histology  and  Pathology. 
SCHLEIF'S  Materia  Medica,  Therapeutics,  Medical  Latin,  etc.  MALS- 
BARY'S  Practice  of  Medicine.  COLLINS'  Diagnosis.  POTTS'  Nervous 
and  Mental  Diseases.  GALLAUDET'S  Surgery.  LIKES'  Genito- 
Urinary  and  Venereal  Diseases.  GRINDON'S  Dermatology.  BALLKN- 
GER  and  WIPPERN'S  Diseases  of  the  Eve,  Ear,  Throat  and  Nose. 
EVANS'  Obstetrics.  CROCKETT'S  Gynecology.  TUTTLK'S  Diseases  of 
Children. 

For  separate  notices  see  under  various  authors'  names. 

LEA  (HENRY  C.).  A  HISTORY  OF  AURICULAR  CONFESSION 
AND  INDULGENCES  IN  THE  LATIN  CHURCH.  In  three 
octavo  volumes  of  about  500  pages  each.  Per  volume,  cloth,  $3.00. 

CHAPTERS  FROM  THE  RELIGIOUS  HISTORY  OF  SPAIN; 

CENSORSHIP  OF  THE  PRESS;  MYSTICS  AND  ILLUMINATI- 
THE  ENDEMONIADAS;  EL  SANTO  NlftO  DE  LA  GUARDIA; 
BRIANDA  DE  BARDAXI.  12mo.,  522  pages.  Cloth,  $2.50. 

FORMULARY  OF  THE  PAPAL  PENITENTIARY.    In  one 

octavo  volume  of  221  pages,  with  frontispiece.    Cloth,  $2.50. 

SUPERSTITION  AND  FORCE;  ESSAYS  ON  THE  WAGER 

OF  LAW,  THE  WAGER  OF  BATTLE,  THE  ORDEAL  AND 
TORTURE.  Fourth  edition,  thoroughly  revised.  In  one  hand- 
some royal  12mo.  volume  of  629  pages.  Cloth,  $2.75. 

STUDIES  IN  CHURCH  HISTORY.    The  Rise  of  the  Temporal 

Power— Benefit  of  Clergy— Excommunication.  New  edition.  In  one 
handsome  12mo.  volume  of  605  pages.  Cloth,  $2.50. 

AN  HISTORICAL  SKETCH  OF  SACERDOTAL  CELIBACY 

IN  THE  CHRISTIAN  CHURCH.  Second  edition.  In  one  hand- 
some octavo  volume  of  685  pages.  Cloth,  $4.50. 

LEHMANN  (C.  G.).  A  MANUAL  OF  CHEMICAL  PHYSIOLOGY. 
In  one  8vo.  volume  of  327  pages,  with  41  engravings.  Cloth,  $2.25, 


LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  "XORK.     19 


LIKES  (SYLVAN  H.).  A  POCKET  TEXT-BOOK  OF  GENITO- 
URINARY AND  VENEREAL  DISEASES.  In  one  handsome 
12rao.  volume  of  about  350  pages,  with  many  illustrations.  Shortly. 
Cloth,  $1.50,  net.  Lea's  Series  of  Pocket  Text-books,  edited  by  BEEN 
B.  GALLAUDET,  M.  D.  See  page  18. 

LOOMIS     (ALFRED    L.)    AND   THOMPSON    (W.   OILMAN, 

EDITORS).  A  SYSTEM  OF  PRACTICAL  MEDICINE.  In 
Contributions  by  Various  American  Authors.  In  four  very  hand- 
some octavo  volumes  of  about  900  pages  each,  fully  illustrated  in 
in  black  and  colors.  Complete  work  now  ready.  Per  volume,  cloth, 
$5 ;  leather,  $6 ;  half  Morocco,  $7.  For  sale  by  subscription  only. 
Full  prospectus  free  on  application  to  the  Publishers.  See  American 
System  of  Practical  Medicine,  page  2. 


LUFF  (ARTHUR  P.). 

Students  of  Medicine, 
engravings.    Cloth,  $2. 


MANUAL  OF  CHEMISTRY,  for  the  use  of 
In  one  12mo.  volume  of  522  pages,  with  36 
See  Student's  Series  of  Manuals,  page  27. 


LYMAN  (HENRY  M.).    THE  PRACTICE  OF  MEDICINE.    In  one 

very  handsome  octavo  volume  of  925  pages,  with  170  engravings. 
Cloth,  $4.75 ;  leather,  $5.75. 

Complete,  concise,  fully  abreast  of  i  Practical,  systematic,  complete  and 
the  times  and  needed  by  all  students  well  balanced. — Chicago  Med.  Re- 
and  practitioners. —  Univ.  Med.  Mag.  corder. 

An  exceedingly  valuable  text-book.  ' 


LYONS  (ROBERT  D.).    A  TREATISE  ON  FEVER.    In  one  octavo 
volume  of  362  pages.    Cloth,  $2.25. 

MACKENZIE  (JOHN  NOLAND).  ON  THE  NOSE  AND  THROAT. 

Handsome  octavo,  about  600  pages,  richly  illustrated.    Preparing. 


MAISCH  (JOHN  M.).  A  MANUAL  OF  ORGANIC  MATERIA 
MEDICA.  New  (7th)  edition,  thoroughly  revised  by  H.  C.  C.  MAISCH, 
Ph.  G.,  Ph.  D.  In  one  very  handsome  12mo.  volume  of  512  pages,  with 
285  engravings.  Just  ready.  Cloth,  $2.50,  net. 


Used  as  text-book  in  every  college 
of  pharmacy  in  the  United  States 
and  recommended  in  medical  col- 
leges.— American  Therapist. 

Noted  on  both  sides  of  the  Atlantic 
and  esteemed  as  much  in  Germany  as 


in  America.  The  work  has  no  equal. 
— Dominion  Med.  Monthly. 

The  best  handbook  upon  phar- 
macognosy  of  any  published  in  this 
country. — Boston  Med.  &  Sur.  Jonr. 


LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK. 


MALSBARY  (GEORGE  E.).  A  POCKET  TEXT-BOOK  OF 
THEORY  AND  PRACTICE  OF  MEDICINE.  In  one  handsome 
12mo.  volume  of  about  350  pages.  Cloth,  $1.50,  net.  Shortly.  Lea's 
»r/Vx  of  Pocket  Text-books,  edited  by  BERN  B.  GALLAUDET,  M.  D. 
See  page  18. 

MANUALS.  See  Students  Quiz  Series,  page  27,  Student's  Series  of 
Manuals,  page  27,  and  Series  of  Clinical  Manuals,  page  25. 

MARSH  (HOWARD).  DISEASES  OF  THE  JOINTS.  In  one  12mo. 
volume  of  468  pages,  with  64  engravings  and  a  colored  plate.  Cloth,  $2. 
See  Series  of  Clinical  Manuals,  page  25. 

MARTIN  (EDWARD).  A  MANUAL  OF  SURGICAL  DIAGNOSIS. 
In  one  12mo.  volume  of  about  400  pp.,  fully  illustrated.  Preparing. 

MARTIN  (WALTON)  AND  ROCKWELL,  (WM.  H.).  A  POCKET 
TEXT-BOOK  OF  CHEMISTRY  AND  PHYSICS.  In  one  hand- 
some 12mo.  volume  of  about  350  pages,  with  many  illustrations.  Cloth, 
$1.50,  net.  Shortly.  Lea's  Series  of  Pnr/.-rf  Text-books,  edited  by 
I'.KKN  B.  GALLAUDET,  M.  D.  See  page  18. 

MAY  (C.  H.).    MANUAL  OF  THE  DISEASES  OF  WOMEN.    For 

the  use  of  Students  and  Practitioners.  Second  edition,  revised  by  L. 
S.  RAU,  M.  D.  In  one  12mo.  volume  of  360  pages,  with  31  engrav- 
ings. Cloth,  $1.75. 

MEDICAL  NEWS  POCKET  FORMULARY,  see  page  32. 

MITCHELL  (S.  WEIR).  CLINICAL  LESSONS  ON  NERVOUS 
DISEASES.  In  one  12mo.  volume  of  299  pages,  with  19  engravings 
and  2  colored  plates.  Cloth,  $2.50.  Of  the  hundred  numbered  copies 
with  the  Author's  signed  title  page  a  few  remain ;  these  are  offered 
in  green  cloth,  gilt  top,  at  $3.50,  net. 


The  book  treats  of  hysteria,  recur- 
rent melancholia,  disorders  of  sleep, 
choreic  movements,  false  sensations 
of  cold,  ataxia,  hemiplegic  pain, 
treatment  of  sciatica,  erytnromelal- 
gia,  reflex  ocularneurosis,  hysteric 


contractions,  rotary  movements  in 
the  feeble  minded,  etc.  Few  can 
speak  with  more  authority  than  the 
author. — The  Journal  of  the  Ameri- 
can Medical  Association. 


MITCHELL  (JOHN  K.).  REMOTE  CONSEQUENCES  OF  IN- 
JURIES OF  NERVES  AND  THEIR  TREATMENT.  In  one 
handsome  12mo.  volume  of  239  pages, with  12  illustrations.  Cloth,  $1.75. 


Injuries  of  the  nerves  are  of  fre- 
quent occurrence  in  private  practice, 
and  often  the  cause  of  intractable 
and  painful  conditions,  conse- 
quently this  volume  is  of  especial 
interest.  Doctor  Mitchell  has  had 


access  to  hospital  records  for  the  last 
thirty  years,  as  well  as  to  the 
government  documents,  and  has 
skilfully  utilized  his  opportunities. 
— The  Med.  Age. 


MORRIS  (MALCOLM).  DISEASES  OF  THE  SKIN.  New  (2d) 
edition.  In  one  12mo.  volume  of  601  pages,  with  10  chromo-litho- 
graphic  plates  and  26  engravings.  Cloth,  $3.25,  net.  Just  ready. 

MULLER  (J.).  PRINCIPLES  OF  PHYSICS  AND  METEOROL- 
OGY. In  one  large  8yo.  vol.  of  623  pages,  with  638  cuts.  Cloth,  $4.50. 


LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK.     21 


MUSSER  (JOHN  H.).   A  PEACTICAL  TEEATISE  ON  MEDICAL 
DIAGNOSIS,  for  Students  and  Physicians.    New  (3d)  edition,  thor- 
oughly revised.    In  one  octavo  volume  of  about  1000  pages,  with  about 
220  engravings  and  48  full-page  colored  plates.    In  press. 
Notices  of  previous  edition  are  appended. 


We  have  no  work  of  equal  value 
in  English.  —  University  Medical 
Magazine. 

His  descriptions  of  the  diagnostic 
manifestations  of  diseases  are  accu- 
rate. This  work  will  meet  all  the 
requirements  of  student  and  physi- 
cian.— The  Medical  News. 

From  its  pages  may  be  made  the 
diagnosis  of  every  malady  that 
afflicts  the  human  body,  including 
those  which  in  general  are  dealt 
with  only  by  the  specialist. — North- 
western Lancet. 


It  so  thoroughly  meets  the  precise 
demands  incident  to  modern  research 
that  it  has  been  adopted  as  a  leading 
text-book  by  the  medical  colleges 
of  this  country. — North  American 
Practitioner. 

Occupies  the  foremost  place  as  a 
thorough,  systematic  treatise. —  Ohio 
Medical  Journal. 

The  best  of  its  kind,  invaluable  to 
the  student,  general  practitioner  and 
teacher. — Montreal  Medical  Journal. 


NATIONAL  DISPENSATORY.  See  Stille,  Maisch  &  Caspari,  p.  27. 

NATIONAL  FORMULARY.  See  Stille,  Maisch  &  Caspari' 8  National 
Dispensatory,  page  27. 

NATIONAL  MEDICAL  DICTIONARY.    See  Billings,  page  4. 

NETTLESHIP  (E.).  DISEASES  OF  THE  EYE.  New  (5th)  American 
from  sixth  English  edition,  thoroughly  revised.  In  one  12mo.  volume 
of  521  pages,  with  161  engravings,  and  2  colored  plates,  test-types, 
formulae  and  color-blindness  test.  Cloth,  $2.25.  Just  ready. 


By  far  the  best  student's  text-book 
on  the  subject  of  ophthalmology  and 
is  conveniently  and  concisely  ar- 
ranged.—  The  Clinical  Review. 

It  has  been  conceded  by  ophthal- 
mologists generally  that  this  work 
for  compactness,  practicality  and 
clearness  has  no  superior  in  the 


English     language.  —  Journal      of 
Medicine  and  Science. 

The  present  edition  is  the  result 
of  revision  both  in  England  and 
America,  and  therefore  contains  the 
latest  and  best  ophthalmological 
ideas  of  both  continents.— The  Phy- 
sician and  Surgeon. 


NICHOLS  (JOHN  B.)  AND  VALE  (F.  P.).  A  POCKET  TEXT- 
BOOK OF  HISTOLOGY  AND  PATHOLOGY.  In  one  handsome 
12mo.  volume  of  about  350  pages,  with  many  illustrations.  In  press. 
Cloth,  $1.50,  net.  Lea's  Series  of  Pocket  Text-books,  edited  by  BERN 
B.  GALLATJDET,  M.  D.  See  page  18. 

NORRIS  (WM.  F.)  AND  OLIVER  (CHAS.  A.).  TEXT-BOOK  OF 
OPHTHALMOLOGY.  In  one  octavo  volume  of  641  pages,  with  357 
engravings  and  5  colored  plates.  Cloth,  $5  ;  leather,  $6. 

A  safe  and  admirable  guide,  well  best,  the  safest  and  the  most  conif  re- 
qualified  to  furnish  a  working  he nsive  volume  upon  the  subject  that 
knowledge  of  ophthalmology.  —  has  ever  been  offered  to  the  Ainer- 
Johns  Hopkins  Hospital  Bulletin.  ican  medical  public. — Annals  of 

It   is  practical  in   its  teachings.  Ophthalmology  and  Otology. 
We  unreservedly  endorse  it  as  the 


22     LEA  BROTHKBS  &  Co.,  PHILADELPHIA  AND  NEW  YOBK. 

OWEN  (EDMUND).  SURGICAL  DISEASES  OF  CHILDREN. 
In  one  12mo.  volume  of  525  pages,  with  85  engravings  and  4  colored 
plates.  Cloth,  $2.  See  Series  of  Clinical  Manuals,  page  25. 


PARK  (ROSWEL.L.).  A  TREATISE  ON  SURGERY  BY  AMERI- 
CAN AUTHORS.  New  and  condensed  edition.  JH  /y/vxx.  In  one 
royal  octavo  volume  of  about  1250  pages,  witli  about  1000  engravings 
and  many  full-page  plates.  J£S7'  This  work  is  also  published  in  a 
larger  edition,  comprising  two  volumes.  Volume  I.,  General  Suryery, 
799  pages,  with  356  engravings  and  21  full-page  plates,  in  colors  and 
monochrome.  Volume  II.,  Special  Surycry,  800  pages,  with  430  engra- 
vings and  17  full-page  plates,  in  colors  and  monochrome.  Per  volume, 
cloth,  $4.50 ;  leather,  $5.50.  Net. 

The  work  is  fresh,  clear  and  practi-  way  that  they  add  great  force  to  the 
cal,  covering  the  ground  thoroughly  j  text.— The  Chicago  Medical  Re- 
yet  briefly,  and  well  arranged  for  !  corder. 

rapid  reference,  so  that  it  will  be  of  The  various  writers  have  em- 
special  value  to  the  student  and  busy  bodied  the  teachings  accepted  at 
practitioner.  The  pathology  is  the  present  hour.— The  North  Amer- 
oroad,  clear  and  scientific,  while  the  ican  Practitioner. 
suggestions  upon  treatment  are  Both  for  the  student  and  practi- 
clear-cut,  thoroughly  modern  and  tioner  it  is  most  valuable.  It  is 
admirably  resourceful.— Johns  Hop-  I  thoroughly  practical  and  yet  thor- 
kins  Hospital  Bulletin.  oughly  scientific. — Medical  News. 

The  latest  and  best  work  written       A  truly  modern  surgery,  not  only 


upon  the  science  and  art  of  surgery. 
Columbus  Medical  Journal. 

The  illustrations  are  almost  en- 
tirely new  and  executed  in  such  a 


in  pathology,  but  also  in  sound 
surgical  therapeutics.  —  New  Or- 
leans Med.  and  Surgical  Journal. 


PARK  (WILLIAM  H.).  BACTERIOLOGY  IN  MEDICINE  AND 
SURGERY.  12mo.,  about  550  pages,  fully  illustrated.  In  press. 

PARRY  (JOHN  S.).  EXTRA-UTERINE  PREGNANCY,  ITS 
CLINICAL  HISTORY,  DIAGNOSIS,  PROGNOSIS  AND  TREAT- 
MENT. In  one  octavo  volume  of  272  pages.  Cloth,  $2.50. 


PARVIN  (THEOPHIL.US).  THE  SCIENCE  AND  ART  OF  OB- 
STETRICS. Third  edition.  In  one  handsome  octavo  volume  of 
677  pages,  with  267  engravings  and  2  colored  plates.  Cloth,  $4.25 ; 
leather,  $5.25. 


In  the  foremost  rank  among  the 
most  practical  and  scientific  medical 
works  of  the  day.— Medical  News. 

It  ranks  second  to  none  in  the 
English  language. — Annals  of  Gyne- 
cology  and  Pediatry. 

The  book  is  complete  in  every  de- 
partment, and  contains  all  the  neces- 
sary detail  required  by  the  modern 


practising  obstetrician.  —  Interna- 
tional Medical  Magazine. 

Parvin's  work  is  practical,  con- 
cise and  comprehensive.  We  com- 
mend it  as  first  of  its  class  in  the 
English  language. — Medical  Fort- 
nightly. 

It  is  an  admirable  text-book  in 
every  sense  of  the  \vord.-Nashville 
Journal  of  Medicine  and  Surgery. 


LEA  BKOTHEKS  &  Co.,  PHILADELPHIA  AND  NEW  YOKK.     23 

PEPPER'S  SYSTEM  OF  MEDICINE.    See  page  3. 

PEPPER  (A.  J.).    FORENSIC  MEDICINE.   In  press.    See  Student's 

Series  of  Manuals,  page  27. 

—  SURGICAL  PATHOLOGY.    In  one  12mo.  volume  of  511  pages, 
with  81  engravings.   Cloth,  $2.   See  Student's  Series  of  Manuals,  p.  27. 

PICK  (T.  PICKERING).      FRACTURES  AND  DISLOCATIONS. 

In  one  12mo.  volume  of  530  pages,  with  93  engravings.      Cloth,  $2. 
See  Series  of  Clinical  Manuals,  page  25. 

PLAYFAIR  (W.  S.).  A  TREATISE  ON  THE  SCIENCE  AND 
PRACTICE  OF  MIDWIFERY.  Seventh  American  from  the  ninth 
English  edition.  In  one  octavo  volume  of  700  pages,  with  207 
engravings  and  7  plates.  Cloth,  $3.75  net;  leather,  $4.75,  net.  Just 
ready. 

In  the  numerous  editions  which    obstetrician.    It  holds  a  place  among 

the  ablest  English-speaking  authori- 


have  appeared  it  has  been  kept  con- 
stantly in  the  foremost  rank.  It  is 
a  work  which  can  be  conscientiously 
recommended  to  the  profession. — 
The  Albany  Medical  Annals. 

This  work  must  occupy  a  fore- 
most place  in  obstetric  medicine  as 
a  safe  guide  to  both  student  and 


ties  on  the  obstetric    &rt.— Buffalo 
Medical  and  Surgical  Journal. 

An  epitome  of  the  science  and 
practice  of  midwifery,  which  em- 
bodies all  recent  advances.  — •  The 
Medical  Fortnightly. 


THE  SYSTEMATIC  TREATMENT  OF  NERVE  PROSTRA- 
TION AND  HYSTERIA.  In  one  12mo.  volume  of  97  pages. 
Cloth,  $1. 

POCKET  FORMULARY,  see  page  32. 
POCKET  TEXT-BOOKS,  see  page  18. 

POL.ITZER  (ADAM).  A  TEXT-BOOK  OF  THE  DISEASES  OF  THE 
EAR  AND  ADJACENT  ORGANS.  Second  American  from  the 
third  German  edition.  Translated  by  OSCAR  DODD,  M.  D.,  and 
edited  by  SIR  WILLIAM  DALEY,  F.  R.  C.  S.  In  one  octavo  volume  of 
748  pages,  with  330  original  engravings.  Cloth,  $5.50. 

The   anatomy  and    physiology  of  ment  are  clear  and  reliable.     We 


each  part  of  the  organ  of  hearing 
are  carefully  considered,  and  then 
follows  an  enumeration  of  the  dis- 
eases to  which  that  special  part  of 
the  auditory  apparatus  is  especially 
liable.  The  indications  for  treat- 


can  confidently  recommend  it,  for  it 
contains  all  that  is  known  upon  the 
subject. — London  Lancet. 

A  safe  and  elaborate  guide  into 
every  part  of  otology. — American 
Journal  of  the  Medical  Sciences. 


POTTS  (CHARLES  S.).  A  POCKET  TEXT-BOOK.  OF  NERVOUS 
AND  MENTAL  DISEASES.  In  one  handsome  12ino.  volume  of 
about  450  pages.  Cloth,  $1.50,  net.  Shortly.  Lea's  Series  of  Pocket 
Text-books,  edited  by  BERN  B.  GALLAUDET,  M.  D.  See  page  18. 

PROGRESSIVE  MEDICINE,  see  page  32. 

PURDY  (CHARLES  WA  BRIGHT'S  DISEASE  AND  ALLIED 
AFFECTIONS  OF  THE  KIDNEY.  In  one  octavo  volume  of  288 
pages,  with  18  engravings.  Cloth,  $2. 


24     LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK. 

PYE-SMITH  (PHILIP  H.).     DISEASES  OF  THE  SKIN.     In  one 

12mo.  vol.  of  407  pp.,  with  28  illus.,  18  of  which  are  colored.  Cloth,  $2. 

QUIZ  SERIES.    See  Student's  Quiz  Series,  page  27. 

KALFE  (CHARLES  H.).  CLINICAL  CHEMISTRY.  In  one 
12mo.  volume  of  314  pages,  with  16  engravings.  Cloth,  $1.50.  See 
Student's  Series  of  Manuals,  page  27. 

RAMSBOTHAM  (FRANCIS  H.).  THE  PRINCIPLES  AND  PRAC- 
TICE OF  OBSTETRIC  MEDICINE  AND  SURGERY.  In  one 
imperial  octavo  volume  of  640  pages,  with  64  plates  and  numerous 
engravings  in  the  text.  Strongly  bound  in  leather,  $7. 

REICHERT  (EDWARD  T.).  A  TEXT-BOOK  ON  PHYSIOLOGY. 
In  one  handsome  octavo  volume  of  about  800  pages,  richly  illustrated. 
Preparing. 

REMSEN  (IRA).  THE  PRINCIPLES  OF  THEORETICAL  CHEM- 
ISTRY. New  (5th)  edition,  thoroughly  revised.  In  one  12mo.  vol- 
ume of  326  pages.  Cloth,  $2. 

A  clear  and  concise  explanation  that  the  work  has  met  with  general 
of  a  difficult  subject.  We  cordially  favor.  This  is  further  established 
recommend  it. — The  London  Lancet.  \  by  the  fact  that  it  has  been  trans- 

The  book  is  equally  adapted  to  the    lated  into  German  and  Italian.    The 


student  of  chemistry  or  the  practi- 
tioner who  desires  to  broaden  his 
theoretical  knowledge  of  chemistry. 
— New  Orleans  Med.  and  Surg.  Jour. 
The  appearance  of  a  fifth  edition 
of  this  treatise  is  in  itself  a  guarantee 


treatise  is  especially  adapted  to  the 
laboratory  student.  It  ranks  unusu- 
ally high  among  the  works  of  this 
class.  This  edition  has  been  brought 
fully  up  to  the  times. — American 
Medico-Surgical  Bulletin. 


RICHARDSON  (BENJAMIN  WARD).  PREVENTIVE  MEDI- 
CINE. In  one  octavo  volume  of  729  pages.  Cloth,  $4 ;  leather,  $5. 

ROBERTS  (JOHN  B.).  THE  PRINCIPLES  AND  PRACTICE  OF 
MODERN  SURGERY.  New  (2d)  edition.  In  one  octavo  volume  of 
about  800  pages,  with  about  500  engravings.  Shortly. 

THE  COMPEND  OF  ANATOMY.     For  use  in  the  Dissecting 

Room  and  in  preparing  for  Examinations.    In  one  16mo.  volume  of 
196  pages.    Limp  cloth,  75  cents. 

ROBERTS  (SIR  WILLIAM).  A  PRACTICAL  TREATISE  ON 
URINARY  AND  RENAL  DISEASES,  INCLUDING  URINARY 
DEPOSITS.  Fourth  American  from  the  fourth  London  edition.  In 
one  very  handsome  8vo.  vol.  of  609  pp.,  with  81  illus.  Cloth,  $3.50. 

ROBERTSON  (J.  MCGREGOR).  PHYSIOLOGICAL  PHYSICS. 
In  one  12mo.  volume  of  537  pages,  with  219  engravings.  Cloth,  $2. 
See  Student's  Series  of  Manuals,  page  27. 

ROSS  (JAMES).  A  HANDBOOK  OF  THE  DISEASES  OF  THE 
NERVOUS  SYSTEM.  In  one  handsome  octavo  volume  of  726  pagee, 
with  184  engravings.  Cloth,  $4.50 ;  leather,  $5.50. 

SAVAGE  (GEORGE  H.).  INSANITY  AND  ALLIED  NEUROSES, 
PRACTICAL  AND  CLINICAL.  In  one  12mo.  volume  of  551  pages, 
with  18.  typical  engravings.  Cloth,  $2.  See  Series  of  Clinical  Man- 
ualt,  page  25. 


LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK.     25 

SCHAFER  (EDWARD  A.).  THE  ESSENTIALS  OF  HISTOL- 
OGY, DESCRIPTIVE  AND  PRACTICAL.  For  the  use  of  Students. 
New  (5th)  edition.  In  one  handsome  octavo  volume  of  359  pages, 
with  392  illustrations.  Cloth,  $3.00,  net.  Just  ready. 


Nowhere  else  will  the  same  very 
moderate  outlay  secure  as  thoroughly 
useful  and  interesting  an  atlas  of 
structural  anatomy. —  The  American 
Journal  of  the  Medical  Sciences. 


The  most  satisfactory  elementary 
text-book  of  histology  in  the  Eng- 
lish language. — The  Boston Med.  and 
Sur.  Jour. 


—  A  COURSE  OF  PRACTICAL  HISTOLOGY.    New(2d)  edition. 
In  one  12mo.  volume  of  307  pages,  with  59  engravings.   Cloth,  $2.25. 


The  book  very  nearly  approaches 
perfection.  Methods  are  given  with 
an  accuracy  of  detail  and  prevision 
of  difficulties  which  can  hardly  be 


overpraised.  It  bears  eloquent  tes- 
timony to  the  wide  knowledge  and 
untiring  industry  of  its  author. — 
The  Scottish  Med.  and  Surg.  Jour. 


SCHLEIF  (WILLIAM).  MATERIA  MEDICA,  THERAPEUTICS, 
PRESCRIPTION  WRITING,  MEDICAL  LATIN,  ETC.  12mo., 

352  pages.     Cloth,  $1.50,  net.    Just  ready.    Lea's  Series  of  Pocket 
Text-books.    Edited  by  BERN  B.  GALLATJDET,  M.  D.    See  page  18. 

SOHMITZ  AND  ZUMPT'S  CLASSICAL  SERIES.  Advanced 
Latin  Exercises.  Cloth,  60  cts.  Schmidt's  Elementary  Latin  Exer- 
cises. Cloth,  50  cents.  Sallust.  Cloth,  60  cents.  Nepos.  Cloth,  60 
cents.  Virgil.  Cloth,  85  cents.  Curtius.  Cloth,  80  cents. 

SCHOFIELD    (ALFRED    T.).      ELEMENTARY    PHYSIOLOGY 
•    FOR  STUDENTS.        In  one  12mo.  volume  of  380  pages,  with  227 
engravings  and  2  colored  plates.     Cloth,  $2. 

SCHREIBER  (JOSEPH).  A  MANUAL  OF  TREATMENT  BY 
MASSAGE  AND  METHODICAL  MUSCLE  EXERCISE.  Octavo 
volume  of  274  pages,  with  117  engravings. 

SENN  (NICHOLAS).  SURGICAL  BACTERIOLOGY.  Second  edi- 
tion. In  one  octavo  volume  of  268  pages,  with  13  plates,  10  of  which 
are  colored,  and  9  engravings.  Cloth,  $2. 

SERIES  OF  CLINICAL  MANUALS.  A  Series  of  Authoritative 
Monographs  on  Important  Clinical  Subjects,  in  12mo.  volumes  of  about 
550  pages,  well  illustrated.  The  following  volumes  are  now  ready : 
YEO  on  Food  in  Health  and  Disease,  new  (2d)  edition,  $2.50;  CARTER 
and  FROST'S  Ophthalmic  Surgery,  $2.25 ;  HUTCHINSON  on  Syphilis, 
$2.25;  MARSH  on  Diseases  of  the  Joints,  $2;  OWEN  on  Surgical  Dis- 
eases of  Children,  $2;  PICK  on  Fractures  and  Dislocations,  $2;  SAVAGE 
on  Insanity  and  Allied  Neuroses,  $2. 
For  separate"  notices,  see  under  various  authors'  names. 

SERIES  OF  STUDENT'S  MANUALS.    See  page  27. 

SIMON  (CHARLES  B.).  CLINICAL  DIAGNOSIS,  BY  MICRO- 
SCOPICAL AND  CHEMICAL  METHODS.  New  (2d)  edition.  In 
one  very  handsome  octavo  volume  of  530  pages,  with  135  engravings 
and  14  full-page  colored  plates.  Cloth,  $3.50.  Just  ready. 


This  book  thoroughly  deserves  its 
success.  It  is  a  very  complete,  authen- 
tic and  useful  manual  of  the  micro- 
scopical and  chemical  methods 
which  are  employed  in  diagnosis. 
Very  excellent  colored  plates  illus- 
trate this  work. — New  York  Medical 
Journal. 


In  all  respects  entirely  up  to  date. 


spects  entirely  up 
Record. 


— Medical 

The  chapter  on  examination  of 
the  urine  is  the  most  complete  and 
advanced  that  we  know  of  in  the 
English  language. —  Canadian  Prac- 
titioner, 


26     LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK. 

SIMON  (W.).  MANUAL  OF  CHEMISTRY.  A  Guide  to  Lectures 
and  Laboratory  Work  for  Beginners  in  Chemistry.  A  Text-book 
specially  adapted  for  Students  of  Pharmacy  and  Medicine.  New  (6th) 
edition.  In  one  8vo.  volume  of  536  pages,  with  46  engravings  and  8 
plates  showing  colors  of  64  tests.  Cloth,  $3.00,  ><>  t.  Jnut  ready. 

It  is  difficult  to  see  how  a  better  the  covers  of  this  book.— The  North- 

book  could  be  constructed.     No  man  western  Lancet. 

who  devotes  himself  to  the  practice  Its  statements  are  all  clear  and  its 

of  medicine  need  know  more  about  teachings    are  practical. —  Virginia 

chemistry  than  is  contained  between  Med.  Monthly. 

SLADE  (D.  D.).  DIPHTHERIA;  ITS  NATURE  AND  TREAT- 
MENT. Second  edition.  In  one  royal  12mo.  vol.,  158  pp.  Cloth,  $1.25. 

SMITH  (EDWARD).  CONSUMPTION;  ITS  EARLY  AND  REME- 
DIABLE STAGES.  In  one  8vo.  volume  of  253  pp.  Cloth,  $2.25. 

SMITH  (J.  LEWIS).  A  TREATISE  ON  THE  DISEASES  OF  IN- 
FANCY AND  CHILDHOOD.  Eighth  edition,  thoroughly  revised 
and  rewritten  and  much  enlarged.  In  one  large  8vo.  volume  of  983 
pages,  with  273  engravings  and  4  full-page  plates.  Cloth,  $4.50; 
leather,  $5.50. 

The  most  complete  and  satisfac-  j  can  more  than  hold  its  own  against 
tory  text-book  with  which  we  are  [  any  other  work  treating  of  the  same 
acquainted . — American  Gynecologi- 
cal and  Obstetrical  Journal. 

It  truly  is  the  most  evenly  bal- 
anced,   clear    in    description    and 

thorough  in  detail  of  any  of  the  I      For  years  the  leading  text-book  on 
books  published  in  this  country  on    children's    diseases  in    America. — 
this  subject. — Medical  Fortnightly.    Chicago  Medical  Recorder. 
A  treatise  which  in  every  respect 

SMITH  (STEPHEN).  OPERATIVE  SURGERY.  Second  and  thor- 
oughly revised  edition.  In  one  octavo  volume  of  892  pages,  with 
1005  engravings.  Cloth,  $4  ;  leather,  $5. 

dium  for  the  modern  surgeon. — Bos- 
ton Medical  and  Surgical  Journal. 


subject. — American  Medico- Surgica I 
Bulletin. 

A  safe  guide  for  students  and  phy- 
sicians.— The  Am.  Jour,  of  Obstetrics. 


One  of  the  most  satisfactory  works 
on  modern  operative  surgery  yet 
published.  Tne  book  is  a  compen- 

SOLL.Y  (S.  EDWIN).  A  HANDBOOK  OF  MEDICAL  CLIMA- 
TOLOGY. In  one  handsome  octavo  volume  of  462  pages,  with  en- 
gravings and  11  full-page  plates,  5  of  which  are  in  colors.  Cloth,  $4.00. 
Just  ready. 


A  clear  and  lucid  summary  of 
what  is  known  of  climate  in  relation 
to  its  influence  upon  human  beings. 
—  The  Therapeutic  Gazette. 

The  book  is  admirably  planned, 
clearly  written, and  the  author  speaks 
from  an  experience  of  thirty  years  as 


an  accurate  observer  and  practical 
therapeutist. — Maryland  Med.  Jour. 
Every  practitioner  of  medicine 
should  possess  himself  of  a  copy  and 
study  it,  and  we  are  sure  he  will 
never  regret  it. — St.  Louis  Medical 
and  Surgical  Journal. 


ST1LLE  (ALFRED).  CHOLERA;  ITS  ORIGIN,  HISTORY,  CAUS- 
ATION, SYMPTOMS,  LESIONS,  PREVENTION  AND  TREAT- 
MENT. In  one  12mo.  volume  of  163  pages,  with  a  chart  showing 
routes  of  previous  epidemics.  Cloth,  $1.25. 

THERAPEUTICS   AND    MATERIA    MEDICA.      Fourth    and 

revised  edition.      In   two  octavo   volumes,  containing    1936    pages. 
Cloth,  $10;  leather,  $12. 


LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK.     27 

STLLLiB  (ALFRED),  MAISCH  (JOHN  M.)  AND  CASPABI 
(CHAS.  JR.).  THE  NATIONAL  DISPENSATORY:  Containing 
the  Natural  History,  Chemistry,  Pharmacy,  Actions  and  Uses  of 
Medicines,  including  those  recognized  in  the  latest  Pharmacopeias  of 
the  United  States,  Great  Britain  and  Germany,  with  numerous  refer- 
ences to  the  French  Codex.  Fifth  edition,  revised  and  enlarged, 
including  the  new  U.  S.  Pharmacopoeia,  Seventh  Decennial  Revision. 
With  Supplement  containing  the  new  edition  of  the  National  Formu- 
lary. In  one  magnificent  imperial  octavo  volume  of  about  2025  pages, 
with  320  engravings.  Cloth,  $7.25;  leather,  $8.  With  ready  reference 
Thumb-letter  Index.  Cloth,  $7.75  ;  leather,  $8.50. 
Recommended  most  highly  for  the  amount  of  information  contained  in 


physician 
druererist.- 


and    invaluable    to  the 
ruggist. — Therapeutic  Gazette. 
It  is  the  oflicial  guide  for  the  Med- 
ical and  Pharmaceutical  professions. 
— Buffalo  Med.  and  Sur.  Jour. 
The  readiness  with  which  the  vast 


this  work  is  made  available  is  indi- 
cated by  the  twenty-five  thousand 
references  in  the  two  indexes. — Bos- 
ton Medical  and  Surgical  Journal. 
Should  be  recognized  as  a  national 
standard. — North  Am.  Practitioner. 


STIMSON  (LJEWIS  A.).    A  MANUAL  OF  OPERATIVE  SURGERY. 

New  (3d)  edition.    In  one  royal  12mo.  volume  of  614  pages,  with  306 
engravings.     Cloth,  $3.75. 


A  useful  and  practical  guide  for 
all  students  and  practitioners. — Am. 
Journal  of  the  Medical  Sciences. 


The  book  is  worth  the  price  for  the 
illustrations  alone. — Ohio  Medical 
Journal. 


STIMSON  (LEWIS  A.).     A  TREATISE  ON  FRACTURES   AND 

DISLOCATIONS.  In  one  handsome  octavo  volume    of  831  pages, 

with  326  engravings  and  20  plates.    Just  ready.    Cloth,  $5.00,  net  ; 

leather,  $6.00,  net. 

Preeminently   the    authoritative        Taken  as  a  whole,  the  work  is  the 

text-book  upon  the   subject.      The    best  one   in    English     to-day.— £*. 

vast  experience  of  the  author  gives  j  Louis  Medical  and  Surgical  Journal. 

to  his  conclusions  an  unimpeachable  i      Pointed,  practical,  comprehensive, 

value.     The  work  is  profusely  il-  !  exhaustive,  authoritative,  well  writ- 

lustrated.     It  will  be   found  indis-    ten    and    well     arranged. — Denver 

pensable  to  the  student  and  the  prac-    Medical  Times. 

titioner  alike. — The  Medical  Age.    \ 

STUDENT'S  QUIZ  SERIES.  Thirteen  volumes,  convenient,  author- 
itative, well  illustrated,  handsomely  bound  in  cloth.  1.  Anatomy 
(double  number);  2.  Physiology;  3.  Chemistry  and  Physics;  4.  Histol- 
ogy, Pathology,  and  Bacteriology;  5.  Materia  Medica  and  Thera- 
peutics ;  6.  Practice  of  Medicine ;  7.  Surgery  (double  number);  8.  Genito- 


Anatomy  and  Surgery,  which  being  double  numbers  are  priced    at 
$1.75  each.    Full  specimen  circular  on  application  to  publishers. 

STUDENT'S  SERIES  OF  MANUALS.  12mos.  of  from  300-540 
pages,  profusely  illustrated,  and  bound  in  red  limp  cloth.  HERMAN'S 
First  Lines  in  Midwifery,  $1.25;  LUFF'S  Manual  of  Chemistry,  $2; 
BRUCE'S  Materia  Medica  and  Therapeutics  (sixth  edition),  $1.50.  net. 

"RlTT  T  >e       C*i\m-r\avo+\\TO        A  naisvmir       or\(\       "PVnroirilrKTTT-          <fcO!  •         ROBERT- 


BELL'S  Comparative  Anatomy  and  Physiology, 
SON'S  Physiological  Physics,  $2;  GOULD'S  Surgical  Diagnosis,  $2; 
KLEIN'S  Elements  of  Histology  (5th  edition),  $2.00,  net ;  PEPPER'S 
Surgical  Pathology,  $2;  TREVES'  Surgical  Applied  Anatomy,  $2; 
RALFE'S  Clinical  Chemistry,  $1.50;  and  CLARKE  and  LOCKWOOD'S 
Dissector's  Manual,  $1.50.  The  following  is  in  press:  PEPPER'S 
Forensic  Medicine. 
For  separate  notices,  see  under  various  author's  names. 


LEA  BROTHERS  A  Co.,  PHILADELPHIA  AND  NEW  YORK. 


STURGES  (OCTAVIUS).  AN  INTRODUCTION  TO  THE  STUDY 
OF  CLINICAL  MEDICINE.  In  one  12mo.  volume.  Cloth,  $1.25. 

SUTTON  (JOHN  BLAND).  SURGICAL  DISEASES  OF  THE 
OVARIES  AND  FALLOPIAN  TUBES.  Including  Abdominal 
Pregnancy.  In  one  12mo.  volume  of  513  pages,  with  119  engravings 
and  5  colored  plates.  Cloth,  $3. 

TAIT  (LAWSON).  DISEASES  OF  WOMEN  AND  ABDOMINAL 
SURGERY.  In  two  handsome  octavo  volumes.  Vol.  I.  contains  546 
pages  and  3  plates.  Cloth,  $3. 

TANNER  (THOMAS  HAWKES)  ON  THE  SIGNS  AND  DIS- 
EASES OF  PREGNANCY.  From  the  second  English  edition.  In 
one  octavo  volume  of  490  pages,  with  4  colored  plates  and  16  engrav- 
ings. Cloth,  $4.25. 

TAYLOR  (ALFRED  S.).  MEDICAL  JURISPRUDENCE.  New 
American  from  the  twelfth  English  edition,  specially  revised  by  CLARK 
BELL,  ESQ.,  of  the  N.  Y.  Bar.  In  one  8vo.  vol.  of  831  pages,  with  54 
engrs.  and  8  full-page  plates.  Cloth,  $4.50;  leather,  $5.50  Just  ready. 


To  the  student,  as  to  the  physician, 
we  would  say,  get  Taylor  first,  and 
then  add  as  means  and  inclination 
enable  you. — American  Practitioner 
and  News. 

It  is  the  authority  accepted  as 
final  by  the  courts  of  all  English- 
speaking  countries.  This  is  the  im- 
portant consideration  for  medical 
men,  since  in  the  event  of  their 
being  summoned  as  experts  or  wit- 


nesses, it  strongly  behooves  them  to 
be  prepared  according  to  the  princi- 
ples and  practice  everywhere  ac- 
cepted. The  work  will  be  found  to 
be  thorough,  authoritative  and 
modern. — Albany  Law  Journal. 

Probably  the  best  work  on  the 
subject  written  in  the  English  lan- 
guage. The  work  has  been  thor- 
oughly revised  and  is  up  to  date. — 
Pacific  Medical  Journal. 


ON  POISONS  IN  RELATION  TO  MEDICINE  AND  MEDI- 
CAL JURISPRUDENCE.  Third  American  from  the  third  London 
edition.  In  one  octavo  volume  of  788  pages,  with  104  illustrations 
Cloth,  $5.50 ;  leather,  $6.50. 

TAYLOR  (ROBERT  W.).     THE    PATHOLOGY  AND   TREAT- 
MENT OF  VENEREAL  DISEASES.    New  (2d)  edition.    In  one 
very  handsome  octavo  volume  of  about  700  pages,  with  about  200  en- 
gravings and  6  colored  plates.    In  press. 
Notices  of  previous  edition  are  appended. 


By  long  odds  the  best  work  on 
venereal  diseases. — Louisville  Medi- 
cal Monthly. 

In  the  observation  and  treatment 
of  venereal  diseases  his  experience 
has  been  greater  probably  than  that 
of  any  other  practitioner  of  this  con- 
tinent.— New  York  Medical  Journal. 

The  clearest,  most  unbiased  and 
ably  presented  treatise  as  yet  pub- 
lished on  this  vast  subject.— The 
Medical  News. 

Decidedly  the  most  important  and 
authoritative  treatise  on  venereal 


diseases  that  has  in  recent  years  ap- 
peared in  English.— American  Jour- 
nal of  the  Medical  Sciences. 

It  is  a  veritable  storehouse  of  our 
knowledge  of  the  venereal  diseases. 
It  is  commended  as  a  conservative, 
practical,  full  exposition  pf  the 
greatest  value.  —  Chicago  Clinicnl 
Review. 

The  best  work  on  venereal  dis- 
eases in  the  English  language.  It 
is  certainly  above  everything  of  the 
kind.— The  St.  Louis  Medical  and 
Surgical  Journal. 


LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YOBK.     29 

TAYLOR  (ROBERT  W.).  A  PRACTICAL  TREATISE  ON  SEX- 
UAL DISORDERS  IN  THE  MALE  AND  FEMALE.  In  one 
8vo.  vol.  of  448  pp.,  with  73  engravings  and  8  colored  plates.  Cloth. 

$3.    Net. 


It  is  a  timely  boon  to  the  medical 
profession  that  an  observer  of  Dr. 
Taylor's  skill  and  experience  has 
written  a  work  on  this  hitherto 
neglected  and  little  understood  class 
of  diseases  which  places  them  on  a 
scientific  basis  and  renders  them  so 
clear  that  the  physician  who  reads 
its  pages  can  treat  this  class  of 
patients  intelligently.  Sterility  in 


the  female  is  presented  in  an  exhaus- 
tive manner,  all  of  the  causes  pro- 
ducing it  being  described.  The 
author  has  presented  to  the  profes- 
sion the  ablest  and  most  scientific 
work  as  yet  published  on  sexual 
disorders,  and  one  which,  if  carefully 
followed,  will  be  of  unlimited  value 
to  both  physician  and  patient. — 
Medical  News. 


A  CLINICAL  ATLAS  OF  VENEREAL  AND  SKIN  DISEASES. 

Including  Diagnosis,  Prognosis  and  Treatment.  In  eight  large  folio 
parts,  measuring  14  x  18  inches,  and  comprising  213  beautiful  figures 
on  58  full-page  chromo-lithographic  plates,  85  fine  engravings  and  425 
pages  of  text.  Complete  work  now  ready.  Price  per  part,  sewed  in 
heavy  embossed  paper,  $2.50.  Bound  in  one  volume,  half  Russia, 
$27  ;  half  Turkey  Morocco,  $28.  For  sale  by  subscription  only.  Address 
the  publishers.  Specimen  plates  by  mail  on  receipt  of  ten  cents. 

TAYLOR  (SEYMOUR).  INDEX  OF  MEDICINE.  A  Manual  for 
the  use  of  Senior  Students  and  others.  In  one  large  12mo.  volume  of 
802  pages.  Cloth,  $3.75. 

THOMAS  (T.  GAILLARD)  AND  MUNDE  (PAUL.  P.).  A  PRAC 
TICAL  TREATISE  ON  THE  DISEASES  OF  WOMEN.  Sixth 
edition,  thoroughly  revised  by  PAUL  F.  MTTNDE,  M.  D.  In  one 
large  and  handsome  octavo  volume  of  824  pages,  with  347  engravings. 
Cloth,  $5 ;  leather,  $6. 


The  best  practical  treatise  on  the 
subject  in  the  English  language. 
It  will  be  of  especial  value  to  the 
general  practitioner  as  well  as  to  the 
specialist.  The  illustrations  are  very 
satisfactory.  Many  of  them  are  new 
and  are  particularly  clear  and  attrac- 
tive.— Boston  Med.  and  Sur.  Jour. 


This  work,  which  has  already  gone 
through  five  large  editions,  and  has 
been  translated  into  French,  Ger- 
man, Spanish  and  Italian,  is  the 
most  practical  and  at  the  same  time 
the  most  complete  treatise  upon  the 
subject. — The  Archives  of  Gynecol- 
ogy,  Obstetrics  and  Pediatrics. 


THOMPSON  (SIR  HENRY).  CLINICAL  LECTURES  ON  DIS- 
EASES OF  THE  URINARY  ORGANS.  Second  and  revised  edi- 
tion. In  one  octavo  vol.  of  203  pp.,  with  25  engravings.  Cloth,  $2.25. 

THE    PATHOLOGY   AND   TREATMENT  OF   STRICTURE 

OF  THE  URETHRA  AND  URINARY  FISTULA.  From  the 
third  English  edition.  In  one  octavo  volume  of  359  pages,  with  47 
engravings  and  3  lithographic  plates.  Cloth,  $3.50. 

THOMSON  (JOHN).  DISEASES  OF  CHILDREN.  In  one  crown 
octavo  volume  of  350  pages,  with  52  illus.  Cloth,  $1.75,  net.  Just  ready. 

TODD  (ROBERT  BENTLEY).  CLINICAL  LECTURES  ON  CER- 
TAIN ACUTE  DISEASES.  In  one  8vo.  vol.  of  320  pp.,  cloth,  $2.50. 

TREVES  (FREDERICK).  OPERATIVE  SURGERY.  In  two 
8vo.  vols.  containing  1550  pp.,  with  422  illus.  Cloth,  $9 ;  leath.,  $11. 

A  SYSTEM  OF  SURGERY.  In  Contributions  by  Twenty-five 

English  Surgeons.  In  two  large  octavo  volumes.  Vol.  I.,  1178  pages, 
with  463  engravings  and  2  colored  plates.  Vol.  II.,  1120  pages,  with 
487  engravings  and  2  colored  plates.  Complete  work,  cloth,  $16.00. 


30     LEA  BROTHERS  &  Co.,  PHILADELPHIA  AND  NEW  YORK. 

TBEVES  (FREDERICK).  SURGICAL  APPLIED  ANATOMY.  In 
one  12mo.  volume  of  540  pages,  with  61  engravings.  Cloth,  $2.  See 
Student's  Series  of  Manuals,  page  27. 

TDTTLE  (GEORGE  M.).  A  POCKET  TEXT-BOOK  OF  DISEASES 
OF  CHILDREN.  In  one  handsome  12mo.  volume  of  about  :iOO  pages, 
with  many  illustrations.  Cloth,  $1.50,  net.  Shortly.  Lea'*  .SV/vY.s \  of 
Pocket  Text-books,  edited  by  BERN  B.  GALLAUDET,  M.  D.  See  p  18. 

VAUGHAN    (VICTOR    C.)    AND    NOVY    (FREDERICK    G.). 

PTOMAINS,  LEUCOMAINS,  TOXINS  AND  ANTITOXINS, 
or  the  Chemical  Factors  in  the  Causation  of  Disease.  New  (3d)  edition. 
In  one  12mo.  volume  of  603  pages.  Cloth,  $3. 

The  work  has  been  brought  down  j  The  present  edition  has  been  not 
to  date,  and  will  be  found  entirely  only  thoroughly  revised  throughout 
satisfactory. — Journal  of  the  Ameri-  \  but  also  greatly  enlarged,  ample 
can  Medical  Association.  j  consideration  being  given  to  the  new 

The  most  exhaustive  and  most  re-    subjects  of  toxins  and  antitoxins. — 


cent  presentation  of  the  subject. — 
American  Jour,  of  the  Med.  Sciences. 


Tri-State  Medical  Journal. 


VISITING  LIST.  THE  MEDICAL  NEWS  VISITING  LIST  for  1899. 
Four  styles :  Weekly  (dated  for  30  patients);  Monthly  (undated  for 
120  patients  per  month) ;  Perpetual  (undated  for  30  patients  each 
week);  and  Perpetual  (undated  for  60  patients  each  week).  The  60- 
patient  book  consists  of  256  pages  of  assorted  blanks.  The  first  three 
styles  contain  32  pages  of  important  data,  thoroughly  revised,  and 
160  pages  of  assorted  blanks.  Each  in  one  volume,  price,  $1.25. 
With  thumb-letter  index  for  quick  use,  25  cents  extra.  Special  rates 
to  advance-paying  subscribers  to  THE  MEDICAL  NEWS  or  THE 
AMERICAN  JOURNAL  OF  THE  MEDICAL  SCIENCES,  or  both.  See  p.  32. 

WATSON  (THOMAS).  LECTURES  ON  THE  PRINCIPLES  AND 
PRACTICE  OF  PHYSIC.  A  new  American  from  the  fifth  and 
enlarged  English  edition,  with  additions  by  H.  HARTSHORNE,  M.  D. 
In  two  large  8vo.  vols.  of  1840  pp.,  with  190  cute.  Cloth,  $9 ;  leather,  $11. 

WEST  (CHARLES).  LECTURES  ON  THE  DISEASES  PECULIAR 
TO  WOMEN.  Third  American  from  the  third  English  edition.  In 
one  octavo  volume  of  543  pages.  Cloth,  $3.75 ;  leather,  $4.75. 

ON  SOME  DISORDERS  OF  THE   NERVOUS  SYSTEM  IN 

CHILDHOOD.    In  one  small  12mo.  volume  of  127  pages.    Cloth,  $1. 

WHARTON  (HENRY  B.).    MINOR  SURGERY  AND  BANDAG- 
ING.   New  (4th)  edition.    In  one  12mo.  vol.  of  about  600  pages,  with 
about  500  engravings,  many  of  which  are  photographic.    Shortly. 
Notices  of  previous  edition  are  appended. 


We  know  of  no  book  which  more 
thoroughly  or  more  satisfactorily 
covers  the  ground  of  Minor  Surgery 
and  Bandaging. — Brooklyn  Medical 
Journal. 

Well  written,  conveniently  ar- 
ranged and  amply  illustrated.  It 
covers  the  field  so  fully  as  to  render 
it  a  valuable  text-book,  as  well  as  a 


work  of  ready  reference  for  sur- 
geons.— North  Amer.  Practitioner. 
The  part  devoted  to  bandaging  is 
perhaps  the  best  exposition  of  the 
subject  in  the  English  language.  It 
can  be  highly  commended  to  the 
student,  the  practitioner  and  the 
specialist.— The  Chicago  Medical 
Recorder. 


LEA  BEOTHEES  &  Co.,  PHILADELPHIA  AND  NEW  YOBK.     31 

WHITLA  (WILLIAM).  DICTIONARY  OF  TREATMENT,  OR 
THERAPEUTIC  INDEX.  Including  Medical  and  Surgical  Thera- 
peutics. In  one  square  octavo  volume  of  917  pages.  Cloth,  $4. 


WILLIAMS  (DAWSON).  THE  MEDICAL  DISEASES  OF  CHIL- 
DREN. In  one  12mo.  volume  of  629  pages,  with  18  illustrations. 
Just  ready.  Cloth,  $2.50,  net. 


The  descriptions  of  symptoms  are 
full,  and  the  treatment  recommended 
will  meet  general  approval.  Under 
each  disease  are  given  the  symptoms, 


diagnoses,  prognosis,  complications, 
and  treatment.  The  work  is  up  to 
date  in  every  sense. — The  Charlotte 
Medical  Journal. 


WILSON  (ERASMUS).    A    SYSTEM    OF    HUMAN    ANATOMY. 

A  new  and  revised  American  from  the  last  English  edition.  Illustrated 
with  397  engravings.  In  one  octavo  volume  of  616  pages.  Cloth,  $4 ; 
leather,  $5. 


—  THE  STUDENT'S  BOOK  OF  CUTANEOUS  MEDICINE, 
one  12mo.  volume.     Cloth,  $3.50. 


In 


WINCKEL  ON  PATHOLOGY  AND  TREATMENT  OF  CHILDBED. 
Translated  by  JAMES  R.  CHADWICK,  A.  M.,  M.  D.  With  additions 
by  the  Author.  In  one  octavo  volume  of  484  pages.  Cloth,  $4. 

WOHLER'S  OUTLINES  OF  ORGANIC  CHEMISTRY.  Translated 
from  the  eighth  German  edition,  by  IRA  REMSEN,  M.  D.  In  one 
12mo.  volume  of  550  pages.  Cloth,  $3. 

YEAR-BOOK  OF  TREATMENT  FOR  1892,  1893,  1896, 1897  and  1898. 
Critical  Reviews  for  Practitioners  of  Medicine  and  Surgery.  In  con- 
tributions by  25  well-known  medical  writers.  12mos.,  aoout500  pages 
each.  Cloth,  $1.50.  In  combination  with  THE  MEDICAL  NEWS  and 
THE  AMERICAN  JOURNAL  OP  THE  MEDICAL  SCIENCES,  75  cents. 


YEO  (I.  BURNEY).  FOOD  IN  HEALTH  AND  DISEASE.  New 
(2d)  edition.  In  one  12mo.  volume  of  592  pages,  with  4  engravings. 
Cloth,  $2.50.  See  Series  of  Clinical  Manuals,  page  26. 


We  doubt  whether  any  book  on 
dietetics  has  been  of  greater  or  more 
widespread  usefulness  than  has  this 
much-quoted  and  much-consulted 


work  of  Dr.  Yeo's.  The  value  of 
the  work  is  not  to  be  overestimated. 
— New  York  Medical  Journal. 


-  A  MANUAL  OF  MEDICAL  TREATMENT,  OR  CLINICAL 
THERAPEUTICS.  Two  volumes  containing  1275  pages.  Cloth,  $5.50. 


YOUNG  (JAMES  K.).    ORTHOPEDIC  SURGERY.    In    one    8vo. 
volume  of  475  pages,  with  286  illustrations.    Cloth,  $4;  leather,  $5. 

In  studying  the  different  chapters,  j  surgical  specialty  and  every  page 
one  is  impressed  with  the  thorough-  j  abounds  with  evidences  of  prac- 
ness  of  the  work.  The  illustrations  ticality.  It  is  the  clearest  and  most 
are  numerous — the  book  thoroughly  modern  work  upon  this  growing  de- 
practical — Medical  News.  |  partment  of  surgery. — The  Chicago 

It  is  a  thorough,  a  very  cpmpre-  !  Clinical  Review, 
hensive  work  upon  this  legitimate  ! 


PERIODICALS. 


PROGRESSIVE  MEDICINE. 

A  Quarterly  Digest  of  New  Methods,  Discoveries,  and  Improvements 
in  the  Medical  and  Surgical  Sciences  by  Eminent  Authorities.  Edited  by 
Dr.  Hobart  Amory  Hare.  In  four  abundantly  illustrated,  cloth  bound, 
octavo  volumes,  of  400-500  pages  each,  issued  quarterly,  commencing 
March  1st,  1899.  Per  annum  (4  volumes),  $10.00  delivered. 


THE  MEDICAL  NEWS. 

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Each  issue  contains  128  octavo  pages,  fully  illustrated.    The  most 
advanced  and  enterprising  American  exponent  of  scientific  medicine. 


THE  MEDICAL  NEWS  VISITING  LIST. 

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THE  MEDICAL  NEWS  POCKET  FORMULARY. 

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proved methods  of  administering  remedial  agents.  Strongly  bound  in 
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